Novel Intra-Procedural Distensibility Measurement Accurately Predicts Immediate Outcome of Pneumatic Dilatation for Idiopathic Achalasia

OBJECTIVES

Often 2-3 graduated pneumatic dilatations (PD) are required to treat achalasia as there is no current intra-procedural predictor of clinical response. Distensibility measurements using functional lumen imaging probe (FLIP) may provide an intra-procedural predictor of outcome. Our aim was to determine the optimal criterion for esophagogastric junction (EGJ) distensibility measurements during PD that predicts immediate clinical response.

METHODS

EGJ distensibility was prospectively measured using FLIP immediately pre- and post-PD. The EGJ distensibility index (EGJ-DI) was defined as a ratio of the narrowest cross-sectional area and the corresponding intra-bag pressure at 40 ml distension. Immediate and short-term clinical responses were defined as Eckardt score ≤3 assessed 2 weeks Post-PD and at 3-month follow-up, respectively.

RESULTS

In 54 patients, we performed thirty-seven 30 mm; twenty 35 mm and six 40 mm PDs. The short-term response rate to the graded PD was 93% (27/29) in newly diagnosed achalasia; 87% (13/15) and 70% (7/10) in those who had relapsed after previous PD and Heller's Myotomy, respectively. Among those demonstrating an immediate response, EGJ-DI increased by an average of 4.5 mm²/mmHg (95% CI (3.5, 5.5) (P<0.001). Within-subject Δ EGJ-DI was highly predictive of immediate clinical response with AUROC of 0.89 (95% CI [0.80, 0.98], P<0.001). An increment in EGJ-DI of 1.8 mm²/mmHg after a single PD predicts an immediate response with an accuracy of 87%.

CONCLUSIONS

FLIP-measured Δ EGJ-DI is a novel intra-procedural tool that accurately predicts immediate clinical response to PD in achalasia. This technique may potentially dictate an immediate mechanism to "step-up" dilator size within a single endoscopy session.

Abstract S4-04: Overcoming resistance to PI3K inhibitors in PIK3CA mutant breast cancer using CDK4/6 inhibition: Results from a combinatorial drug screen

Various components of the phosphatidylinositol 3-kinase (PI3K) pathway are deregulated across a spectrum of human cancers. Notably, cancers with PIK3CA mutations, seen in roughly 30% of breast cancers, are amongst the most sensitive to PI3K inhibitors (PI3Ki) as single agents. Therefore, there have been great efforts to develop PI3K inhibitors specifically for these types of cancers, and many agents have already entered the clinic.

Although initial responses and prolonged stable disease have been observed, resistance frequently emerges. Moreover, there is a subset of PIK3CA mutated cancers that unexpectedly do not exhibit an initial response or disease stabilization upon exposure to PI3K inhibitors, despite presence of the mutation. These cancers are said to have de novo resistance to PI3K inhibition. To determine methods of overcoming resistance to PI3K inhibitors, we generated two models with acquired resistance to the p110a isoform specific inhibitor BYL-719 (BYL) using MDA-MB-453 (453) and T47D. We also established one model of resistance to the pan-PI3K inhibitor GDC-0941 using MCF7 cells. These lines were chosen because of their PIK3CA mutated status and sensitivity to PI3K inhibition. Each cell line was grown in increasing concentrations of PI3K inhibitor until the cells proliferated readily at a dose of drug that effectively reduced cell viability and inhibited pAKT in the sensitive parental cell lines. Interestingly, both BYL resistant cells (453R and T47DR) were cross resistant GDC and the MCF7R line was refractory to BYL.

To elucidate mechanisms to overcome resistance to PI3K inhibitors, we undertook a combinatorial drug screen, in which PI3K inhibitor resistant cells were treated with escalating doses of a panel of 45 targeted agents, both in the presence and absence of a fixed dose of PI3Ki, to determine which agents synergized effectively with PI3K inhibition in these resistant cells. We observed in each of the three PI3Ki resistant models a synergy between the CDK4/6 inhibitor LEE-011 and PI3K inhibition. We furthermore tested this combination of agents in a PIK3CA mutated breast cancer model with de novo resistance to PI3K inhibitors, CAL51, and again noted efficacy with the combination of GDC and LEE-011 while either agent on its own displayed minimal activity.

To determine whether addition of CDK 4/6 inhibition might be an effective addition to PI3Ki in the upfront setting in vivo, we injected each of the PIK3CA mutated lines MCF7, 453, and T47D into female nude mice and treated with vehicle, BYL, LEE-011, or the combination. We noted in each of the three models that the combination of agents, led to tumor regression that was more substantial than single agent treatment, and furthermore delayed the acquisition of resistance relative to single agent therapy. We furthermore tested GDC with LEE-011 singly and in combination in both MCF7 and CAL51 xenografts and again noted that the combination of agents led to tumor regression, whereas in these instances, single agent treatment did not.

We conclude that the combination of PI3K and CDK 4/6 inhibition may be an effective strategy for treating PIK3CA mutated breast cancer and deserves further study in the clinical setting.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S4-04.

Abstract P3-12-03: Combined targeting of HER2 and VEGFR2 for effective treatment of HER2-amplified breast cancer brain metastases

Brain metastases remain a serious obstacle in the treatment of patients with human epidermal growth factor receptor-2 (HER2)-amplified breast cancer. Unlike HER2-amplified breast tumors growing in extra-cranial locations, brain metastases do not respond well to HER2 inhibitors and are often the reason for treatment failure. One of the major challenges in studying brain metastases is the lack of preclinical models. We developed a HER2-amplified mouse model of brain metastasis using an orthotopic xenograft of BT474 cells in mice. As seen in patients, the HER2 inhibitors trastuzumab and lapatinib failed to contain brain metastatic tumor growth.

Based on previous findings from our laboratory suggesting a role of vascular endothelial growth factor (VEGF) in the resistance of HER2-overexpressing breast cancer brain metastases to trastuzumab, we combined HER2 inhibitors with the anti-VEGFR2 antibody DC101. The combination of either trastuzumab and DC101 or lapatinib and DC101 significantly slowed metastatic tumor growth in the brain, and resulted in a striking improvement in overall survival. The benefit is due largely to an anti-angiogenic effect. The combination of anti-HER2 and anti-VEGFR2 therapy reduced both the total and functional microvascular density in the brain metastatic tumors. Moreover, tumor tissues under combination therapy showed a marked increase in necrosis.

Preclinical and clinical evidence suggest that the combination of trastuzumab and lapatinib is superior to either agent alone – though this has never been tested in the brain metastatic setting. We consistently observed increased phosphorylation of HER2 in breast tumor cells growing in the brain compared with the mammary fat pad. In addition, while short-term lapatinib treatment significantly reduced HER2 activation in the brain, it could do so only to the level of that observed in the untreated mammary fat pad - and this effect disappeared over time. We hypothesized that more pronounced HER2 inhibition would be beneficial to these brain metastases with increased HER2 activation. We show here a significant growth delay with the combination of the two HER2 inhibitors compared with monotherapy. Moreover, we found a dramatic brain metastatic tumor growth delay in mice treated with both HER2 inhibitors, trastuzumab and lapatinib, and DC101. The triple combination prolonged overall survival 5 times longer than control-treated mice.

Brain metastasis from breast cancer is considered the “final frontier” of breast cancer research and treatment. Our findings support the clinical development of a three-drug regimen of trastuzumab, lapatinib and a VEGF pathway inhibitor for the treatment of HER2-amplified breast cancer brain metastases. While the anti-VEGF antibody bevacizumab in combination with trastuzumab and chemotherapy has shown some promise in HER2-positive metastatic breast cancer patient, there are no data on its efficacy in the context of brain metastases. A clinical trial is now recruiting patients to evaluate the efficacy of bevacizumab in breast cancer patients with active brain metastases, including its combination with trastuzumab in patients with HER2-positive disease. This trial may provide clinical evidence for the approach presented here.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-12-03.

Pemetrexed-based chemotherapy in patients with advanced, ALK-positive non-small cell lung cancer

BACKGROUND

Anaplastic lymphoma kinase (ALK)-positive non-small-cell lung cancer (NSCLC) is highly responsive to crizotinib. To determine whether ALK-positive NSCLC is also sensitive to pemetrexed, we retrospectively evaluated progression-free survival (PFS) of ALK-positive versus ALK-negative patients who had been treated with pemetrexed-based chemotherapy for advanced NSCLC.

PATIENTS AND METHODS

We identified 121 patients with advanced, ALK-positive NSCLC in the USA, Australia, and Italy. For comparison, we evaluated 266 patients with advanced, ALK-negative, epidermal growth factor receptor (EGFR)-wild-type NSCLC, including 79 with KRAS mutations and 187 with wild-type KRAS (WT/WT/WT). We determined PFS on different pemetrexed regimens.

RESULTS

Among 70 ALK-positive patients treated with a platinum/pemetrexed regimen, the median PFS (mPFS) was 7.3 months (95% confidence interval (CI) 5.5-9.5). The mPFS of 51 ALK-positive patients treated with single-agent pemetrexed or nonplatinum/pemetrexed combinations was 5.5 months (2.8-9.0). For ALK-negative patients, PFS on all pemetrexed-based regimens was similar to that of ALK-positive patients, except in the specific setting of first-line platinum/pemetrexed where the mPFS was only 4.2 and 5.4 months in KRAS and WT/WT/WT patients, respectively. However, among patients with a never/light-smoking history (0-10 pack-year smoking history) treated with first-line platinum/pemetrexed, there was no difference in PFS between ALK-positive and ALK-negative patients.

CONCLUSIONS

PFS on pemetrexed or nonplatinum/pemetrexed combinations was similar in ALK-positive and ALK-negative patients. PFS on first-line platinum/pemetrexed may be prolonged in never/light-smoking patients regardless of ALK status.

Implementing multiplexed genotyping of non-small-cell lung cancers into routine clinical practice

BACKGROUND

Personalizing non-small-cell lung cancer (NSCLC) therapy toward oncogene addicted pathway inhibition is effective. Hence, the ability to determine a more comprehensive genotype for each case is becoming essential to optimal cancer care.

METHODS

We developed a multiplexed PCR-based assay (SNaPshot) to simultaneously identify >50 mutations in several key NSCLC genes. SNaPshot and FISH for ALK translocations were integrated into routine practice as Clinical Laboratory Improvement Amendments-certified tests. Here, we present analyses of the first 589 patients referred for genotyping.

RESULTS

Pathologic prescreening identified 552 (95%) tumors with sufficient tissue for SNaPshot; 51% had ≥1 mutation identified, most commonly in KRAS (24%), EGFR (13%), PIK3CA (4%) and translocations involving ALK (5%). Unanticipated mutations were observed at lower frequencies in IDH and β-catenin. We observed several associations between genotypes and clinical characteristics, including increased PIK3CA mutations in squamous cell cancers. Genotyping distinguished multiple primary cancers from metastatic disease and steered 78 (22%) of the 353 patients with advanced disease toward a genotype-directed targeted therapy.

CONCLUSIONS

Broad genotyping can be efficiently incorporated into an NSCLC clinic and has great utility in influencing treatment decisions and directing patients toward relevant clinical trials. As more targeted therapies are developed, such multiplexed molecular testing will become a standard part of practice.

H1047R phosphatidylinositol 3-kinase mutant enhances HER2-mediated transformation by heregulin production and activation of HER3

Hyperactivation of phosphatidylinositol-3 kinase (PI3K) can occur as a result of somatic mutations in PIK3CA, the gene encoding the p110α subunit of PI3K. The HER2 oncogene is amplified in 25% of all breast cancers and some of these tumors also harbor PIK3CA mutations. We examined mechanisms by which mutant PI3K can enhance transformation and confer resistance to HER2-directed therapies. We introduced the PI3K mutations E545K and H1047R in MCF10A human mammary epithelial cells that also overexpress HER2. Both mutants conferred a gain of function to MCF10A/HER2 cells. Expression of H1047R PI3K but not E545K PI3K markedly upregulated the HER3/HER4 ligand heregulin (HRG). HRG siRNA inhibited growth of H1047R but not E545K-expressing cells and synergized with the HER2 inhibitors trastuzumab and lapatinib. The PI3K inhibitor BEZ235 markedly inhibited HRG and pAKT levels and, in combination with lapatinib, completely inhibited growth of cells expressing H1047R PI3K. These observations suggest that PI3K mutants enhance HER2-mediated transformation by amplifying the ligand-induced signaling output of the ErbB network. This also counteracts the full effect of therapeutic inhibitors of HER2. These data also suggest that mammary tumors that contain both HER2 gene amplification and PIK3CA mutations should be treated with a combination of HER2 and PI3K inhibitors.

Exon 9 and exon 20 mutations in PIK3CA confer resistance to HER2 inhibitors in HER2-overexpressing breast cancer cells

Abstract #4054

The anti-tumor effect of HER2 antagonists in HER2-dependent breast cancer cells has been proposed to rely on inhibition of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. Mutations in the p110α catalytic subunit of PI3K occur in up to 40% of breast cancers and activation of this pathway has been implicated in resistance to the HER2 antibody trastuzumab (T). PIK3CA mutations cluster in two regions in the helical (E542K, E545K; exon 9) and catalytic (H1047R; exon 20) domains. We studied the role of these mutants in resistance to HER2 inhibitors in breast cancer cells with HER2 amplification. Two lines with endogenous H1047R p110 (PI3K), SUM190 and HCC1954, and SKBR3, SUM225, and BT474 cells stably transduced with retroviral vectors encoding HA-tagged wild-type, E545K, or H1047R p110, were studied for their response to the HER2 tyrosine kinase inhibitor lapatinib ditosylate (L; GW-572016) and T. In monolayer and 3D cell proliferation assays, partial resistance to L and T was conferred by either mutation compared to WT p110. After prolonged L treatment, Ser473 phosphorylation of Akt recovered in all cells with endogenous or ectopic p110 mutants in spite of continued inhibition of Y1248 P-HER2 and Y1289 P-HER3 by L. Further, BT474 cells with either p110 mutant could be passaged in the continued presence of L. Immunoprecipitation of p85, the regulatory subunit of PI3K, showed that PI3K association with HER3 was abrogated by T and L. RNAi of HER3 in MCF10A/HER2/PI3KE545K and MCF10A/HER2/PI3KH1047R cells markedly but not completely inhibited growth suggesting that the PI3K mutants may still depend on HER3 for full activation. We hypothesized that in cells with mutant PI3K, the mutants coexist in a pool with WT enzyme, and that mutant and WT p110α are bound to p85 in variable proportions. Experiments to measure whether the ratio of mutant to WT p110 bound to p85, assayed by mass spectrometry, will increase in the PI3K-mutant cells with acquired resistance to L are in progress. To test the role of these mutants on resistance to anti-HER2 therapies in vivo, athymic mice bearing BT474 xenografts with ectopic WT, E545K, or H1047R p110 are undergoing treatment with L and T. Finally, we analyzed mutations of PIK3CA in a cohort of 40 patients with locally advanced HER2+ breast cancer treated with weekly single-agent T for 3 weeks, followed by T with docetaxel for a total of 12 weeks before surgery (Mohsin et al. JCO 23:2460, 2005). Sequential core biopsies at weeks 1 and 3 after initiation of T were taken. Eight of 40 tumors (20%) expressed mutant PI3K, 2 in exon 9 and 6 in exon 20. PIK3CA mutations did not correlate with change in Ki67 (p=0.97) or cleaved caspase 3 (p=0.51) in weeks 1 or 3 of treatment nor with pathologic complete response (p=0.21). These data suggest that, if mutant PI3K confers relative resistance to T, a shorter time to recurrence may be a more robust endpoint as the initial cellular or clinical response may not be a good indicator of this resistance.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4054.

Caveolin-1 null mice are viable but show evidence of hyperproliferative and vascular abnormalities

Caveolin-1 is the principal structural protein of caveolae membranes in fibroblasts and endothelia. Recently, we have shown that the human CAV-1 gene is localized to a suspected tumor suppressor locus, and mutations in Cav-1 have been implicated in human cancer. Here, we created a caveolin-1 null (CAV-1 -/-) mouse model, using standard homologous recombination techniques, to assess the role of caveolin-1 in caveolae biogenesis, endocytosis, cell proliferation, and endothelial nitric-oxide synthase (eNOS) signaling. Surprisingly, Cav-1 null mice are viable. We show that these mice lack caveolin-1 protein expression and plasmalemmal caveolae. In addition, analysis of cultured fibroblasts from Cav-1 null embryos reveals the following: (i) a loss of caveolin-2 protein expression; (ii) defects in the endocytosis of a known caveolar ligand, i.e. fluorescein isothiocyanate-albumin; and (iii) a hyperproliferative phenotype. Importantly, these phenotypic changes are reversed by recombinant expression of the caveolin-1 cDNA. Furthermore, examination of the lung parenchyma (an endothelial-rich tissue) shows hypercellularity with thickened alveolar septa and an increase in the number of vascular endothelial growth factor receptor (Flk-1)-positive endothelial cells. As predicted, endothelial cells from Cav-1 null mice lack caveolae membranes. Finally, we examined eNOS signaling by measuring the physiological response of aortic rings to various stimuli. Our results indicate that eNOS activity is up-regulated in Cav-1 null animals, and this activity can be blunted by using a specific NOS inhibitor, nitro-l-arginine methyl ester. These findings are in accordance with previous in vitro studies showing that caveolin-1 is an endogenous inhibitor of eNOS. Thus, caveolin-1 expression is required to stabilize the caveolin-2 protein product, to mediate the caveolar endocytosis of specific ligands, to negatively regulate the proliferation of certain cell types, and to provide tonic inhibition of eNOS activity in endothelial cells.

Palmitoylation of caveolin-1 at a single site (Cys-156) controls its coupling to the c-Src tyrosine kinase: targeting of dually acylated molecules (GPI-linked, transmembrane, or cytoplasmic) to caveolae effectively uncouples c-Src and caveolin-1 (TYR-14)

Caveolin-1 was initially identified as a phosphoprotein in Rous sarcoma virus-transformed cells. Previous studies have shown that caveolin-1 is phosphorylated on tyrosine 14 by c-Src and that lipid modification of c-Src is required for this phosphorylation event to occur in vivo. Phosphocaveolin-1 (Tyr(P)-14) localizes within caveolae near focal adhesions and, through its interaction with Grb7, augments anchorage-independent growth and epidermal growth factor-stimulated cell migration. However, the cellular factors that govern the coupling of caveolin-1 to the c-Src tyrosine kinase remain largely unknown. Here, we show that palmitoylation of caveolin-1 at a single site (Cys-156) is required for coupling caveolin-1 to the c-Src tyrosine kinase. Furthermore, upon evaluating a battery of nonreceptor and receptor tyrosine kinases, we demonstrate that the tyrosine phosphorylation of caveolin-1 by c-Src is a highly selective event. We show that Src-induced tyrosine phosphorylation of caveolin-1 can be inhibited or uncoupled by targeting dually acylated proteins (namely carcinoembryonic antigen (CEA), CD36, and the NH(2)-terminal domain of Galpha(i1)) to the exoplasmic, transmembrane, and cytoplasmic regions of the caveolae membrane, respectively. Conversely, when these proteins are not properly targeted or lipid-modified, the ability of c-Src to phosphorylate caveolin-1 remains unaffected. In addition, when purified caveolae preparations are preincubated with a myristoylated peptide derived from the extreme N terminus of c-Src, the tyrosine phosphorylation of caveolin-1 is abrogated; the same peptide lacking myristoylation has no inhibitory activity. However, an analogous myristoylated peptide derived from c-Yes also has no inhibitory activity. Thus, the inhibitory effects of the myristoylated c-Src peptide are both myristoylation-dependent and sequence-specific. Finally, we investigated whether phosphocaveolin-1 (Tyr(P)-14) interacts with the Src homology 2 and/or phosphotyrosine binding domains of Grb7, the only characterized downstream mediator of its function. Taken together, our data identify a series of novel lipid-lipid-based interactions as important regulatory factors for coupling caveolin-1 to the c-Src tyrosine kinase in vivo.

Caveolin-3 null mice show a loss of caveolae, changes in the microdomain distribution of the dystrophin-glycoprotein complex, and t-tubule abnormalities

Caveolin-3, a muscle-specific caveolin-related protein, is the principal structural protein of caveolae membrane domains in striated muscle cells. Recently, we identified a novel autosomal dominant form of limb-girdle muscular dystrophy (LGMD-1C) in humans that is due to mutations within the coding sequence of the human caveolin-3 gene (3p25). These LGMD-1C mutations lead to an approximately 95% reduction in caveolin-3 protein expression, i.e. a caveolin-3 deficiency. Here, we created a caveolin-3 null (CAV3 -/-) mouse model, using standard homologous recombination techniques, to mimic a caveolin-3 deficiency. We show that these mice lack caveolin-3 protein expression and sarcolemmal caveolae membranes. In addition, analysis of skeletal muscle tissue from these caveolin-3 null mice reveals: (i) mild myopathic changes; (ii) an exclusion of the dystrophin-glycoprotein complex from lipid raft domains; and (iii) abnormalities in the organization of the T-tubule system, with dilated and longitudinally oriented T-tubules. These results have clear mechanistic implications for understanding the pathogenesis of LGMD-1C at a molecular level.

Tumor necrosis factor alpha-mediated insulin resistance, but not dedifferentiation, is abrogated by MEK1/2 inhibitors in 3T3-L1 adipocytes

Tumor necrosis factor-alpha (TNFalpha) has been implicated as a contributing mediator of insulin resistance observed in pathophysiological conditions such as obesity, cancer-induced cachexia, and bacterial infections. Previous studies have demonstrated that TNFalpha confers insulin resistance by promoting phosphorylation of serine residues on insulin receptor substrate 1 (IRS-1), thereby diminishing subsequent insulin-induced tyrosine phosphorylation of IRS-1. However, little is known about which signaling molecules are involved in this process in adipocytes and about the temporal sequence of events that ultimately leads to TNFalpha-stimulated IRS-1 serine phosphorylation. In this study, we demonstrate that specific inhibitors of the MAP kinase kinase (MEK)1/2-p42/44 mitogen-activated protein (MAP) kinase pathway restore insulin signaling to normal levels despite the presence of TNFalpha. Additional experiments show that MEK1/2 activity is required for TNFalpha-induced IRS-1 serine phosphorylation, thereby suggesting a mechanism by which these inhibitors restore insulin signaling. We observe that TNFalpha requires 2.5-4 h to markedly reduce insulin-triggered tyrosine phosphorylation of IRS-1 in 3T3-L1 adipocytes. Although TNFalpha activates p42/44 MAP kinase, maximal stimulation is observed within 10-30 min. To our surprise, p42/44 activity returns to basal levels well before IRS-1 serine phosphorylation and insulin resistance are observed. These activation kinetics suggest a mechanism of p42/44 action more complicated than a direct phosphorylation of IRS-1 triggered by the early spike of TNFalpha-induced p42/44 activity. Chronic TNFalpha treatment (>> 72 h) causes adipocyte dedifferentiation, as evidenced by the loss of triglycerides and down-regulation of adipocyte-specific markers. We observe that this longer term TNFalpha-mediated dedifferentiation effect utilizes alternative, p42/44 MAP kinase-independent intracellular pathways. This study suggests that TNFalpha-mediated insulin resistance, but not adipocyte dedifferentiation, is mediated by the MEK1/2-p42/44 MAP kinase pathway.

Gene-target recognition among members of the myc superfamily and implications for oncogenesis

Myc and Mad family proteins regulate multiple biological processes through their capacity to influence gene expression directly. Here we show that the basic regions of Myc and Mad proteins are not functionally equivalent in oncogenesis, have separable E-box-binding activities and engage both common and distinct gene targets. Our data support the view that the opposing biological actions of Myc and Mxi1 extend beyond reciprocal regulation of common gene targets. Identification of differentially regulated gene targets provides a framework for understanding the mechanism through which the Myc superfamily governs the growth, proliferation and survival of normal and neoplastic cells.

Constitutively active mitogen-activated protein kinase kinase 6 (MKK6) or salicylate induces spontaneous 3T3-L1 adipogenesis

Although much has been learned regarding the importance of p38 mitogen-activated protein kinase in inflammatory and stress responses, relatively little is known concerning its role in differentiation processes. Recently, we demonstrated that p38 mitogen-activated protein kinase activity is necessary for the differentiation of 3T3-L1 fibroblasts into adipocytes (Engelman, J. A., Lisanti, M. P., and Scherer, P. E. (1998) J. Biol. Chem. 273, 32111-32120). p38 activity is high during the initial stages of differentiation but decreases drastically as the fibroblasts undergo terminal differentiation into adipocytes. However, it remains unknown whether activation of p38 is sufficient to stimulate adipogenesis and whether the down-regulation of p38 activity in mature adipocytes is critical for maintaining adipocyte homeostasis. In this report, we have directly addressed these questions by analyzing 3T3-L1 cell lines harboring a specific upstream activator of p38 (a constitutively active mitogen-activated protein kinase kinase 6 (MKK6) mutant, MKK6(Glu)) under the control of an inducible promoter. Induction of MKK6(Glu) in 3T3-L1 fibroblasts spurs adipocyte conversion in the absence of the hormonal mixture normally required for efficient differentiation of wild-type cells. However, activation of p38 in adipocytes leads to cell death. Furthermore, treatment of 3T3-L1 fibroblasts with salicylate, a potent stimulator of p38, produces adipocyte-specific changes consistent with those observed with induction of MKK6(Glu). Expression of MKK6(Glu) in NIH-3T3 fibroblasts (cells that do not differentiate into adipocytes under normal conditions) is capable of converting these fibroblasts into lipid-laden fat cells following hormonal stimulation. Thus, p38 activation has pro-adipogenic effects in multiple fibroblast cell lines.

p42/44 MAP kinase-dependent and -independent signaling pathways regulate caveolin-1 gene expression. Activation of Ras-MAP kinase and protein kinase a signaling cascades transcriptionally down-regulates caveolin-1 promoter activity

Caveolin-1 is a principal component of caveolae membranes in vivo. Caveolin-1 mRNA and protein expression are down-regulated in NIH 3T3 cells in response to transformation by activated oncogenes, such as H-Ras(G12V) and v-Abl. The mechanisms governing this down-regulation event remain unknown. Here, we show that caveolin-1 gene expression is directly regulated by activation of the Ras-p42/44 MAP kinase cascade. Down regulation of caveolin-1 protein expression by Ras is independent of (i) the type of activating mutation (G12V versus Q61L) and (ii) the form of activated Ras transfected (H-Ras versus K-Ras versus N-Ras). Treatment of Ras or Raf-transformed NIH 3T3 cells with a well characterized MEK inhibitor (PD 98059) restores caveolin-1 protein expression. In contrast, treatment of v-Src and v-Abl transformed NIH 3T3 cells with PD 98059 does not restore caveolin-1 expression. Thus, there must be at least two pathways for down-regulating caveolin-1 expression: one that is p42/44 MAP kinase-dependent and another that is p42/44 MAP kinase-independent. We focused our efforts on the p42/44 MAP kinase-dependent pathway. The activity of a panel of caveolin-1 promoter constructs was evaluated using transient expression in H-Ras(G12V) transformed NIH 3T3 cells. We show that caveolin-1 promoter activity is up-regulated approximately 5-fold by inhibition of the p42/44 MAP kinase cascade. Using electrophoretic mobility shift assays we provide evidence that the caveolin-1 promoter (from -156 to -561) is differentially bound by transcription factors in normal and H-Ras(G12V)-transformed cells. We also show that activation of protein kinase A (PKA) signaling is sufficient to down-regulate caveolin-1 protein expression and promoter activity. Thus, we have identified two signaling pathways (Ras-p42/44 MAP kinase and PKA) that transcriptionally down-regulate caveolin-1 gene expression.

Targeted down-regulation of caveolin-3 is sufficient to inhibit myotube formation in differentiating C2C12 myoblasts. Transient activation of p38 mitogen-activated protein kinase is required for induction of caveolin-3 expression and subsequent myotube formation

Caveolin-3 is the principal structural protein of caveolae membrane domains in striated muscle cells. Caveolin-3 mRNA and protein expression are dramatically induced during the differentiation of C2C12 skeletal myoblasts, coincident with myoblast fusion. In these myotubes, caveolin-3 localizes to the sarcolemma (muscle cell plasma membrane), where it associates with the dystrophin-glycoprotein complex. However, it remains unknown what role caveolin-3 plays in myoblast differentiation and myotube formation. Here, we employ an antisense approach to derive stable C2C12 myoblasts that fail to express the caveolin-3 protein. We show that C2C12 cells harboring caveolin-3 antisense undergo differentiation and express normal amounts of four muscle-specific marker proteins. However, C2C12 cells harboring caveolin-3 antisense fail to undergo myoblast fusion and, therefore, do not form myotubes. Interestingly, treatment with specific p38 mitogen-activated protein kinase inhibitors blocks both myotube formation and caveolin-3 expression, but does not affect the expression of other muscle-specific proteins. In addition, we find that three human rhabdomyosarcoma cell lines do not express caveolin-3 and fail to undergo myoblast fusion. Taken together, these results support the idea that caveolin-3 expression is required for myoblast fusion and myotube formation, and suggest that p38 is an upstream regulator of caveolin-3 expression.

Expression of caveolin-1 is required for the transport of caveolin-2 to the plasma membrane. Retention of caveolin-2 at the level of the golgi complex

Caveolins-1 and -2 are normally co-expressed, and they form a hetero-oligomeric complex in many cell types. These caveolin hetero-oligomers are thought to represent the assembly units that drive caveolae formation in vivo. However, the functional significance of the interaction between caveolins-1 and -2 remains unknown. Here, we show that caveolin-1 co-expression is required for the transport of caveolin-2 from the Golgi complex to the plasma membrane. We identified a human erythroleukemic cell line, K562, that expresses caveolin-2 but fails to express detectable levels of caveolin-1. This allowed us to stringently assess the effects of recombinant caveolin-1 expression on the behavior of endogenous caveolin-2. We show that expression of caveolin-1 in K562 cells is sufficient to reconstitute the de novo formation of caveolae in these cells. In addition, recombinant expression of caveolin-1 allows caveolin-2 to form high molecular mass oligomers that are targeted to caveolae-enriched membrane fractions. In striking contrast, in the absence of caveolin-1 expression, caveolin-2 forms low molecular mass oligomers that are retained at the level of the Golgi complex. Interestingly, we also show that expression of caveolin-1 in K562 cells dramatically up-regulates the expression of endogenous caveolin-2. Northern blot analysis reveals that caveolin-2 mRNA levels remain constant under these conditions, suggesting that the expression of caveolin-1 stabilizes the caveolin-2 protein. Conversely, transient expression of caveolin-2 in CHO cells is sufficient to up-regulate endogenous caveolin-1 expression. Thus, the formation of a hetero-oligomeric complex between caveolins-1 and -2 stabilizes the caveolin-2 protein product and allows caveolin-2 to be transported from the Golgi complex to the plasma membrane.

Sequence and detailed organization of the human caveolin-1 and -2 genes located near the D7S522 locus (7q31.1). Methylation of a CpG island in the 5' promoter region of the caveolin-1 gene in human breast cancer cell lines

The CA microsatellite repeat marker, D7S522, is located at the center of a approximately 1000 kb smallest common deleted region that is lost in many forms of human cancer. It has been proposed that a putative tumor suppressor gene lies in close proximity to D7S522, within this smallest common deleted region. However, the genes located in proximity to D7S522 have remained elusive. Recently, we identified five independent BAC clones (approximately 100-200 kb) containing D7S522 and the human genes encoding caveolins 1 and 2. Here, we present the detailed organization of the caveolin locus and its relationship to D7S522, as deduced using a shot-gun sequencing approach. We derived two adjacent contigs for a total coverage of approximately 250 kb. Analysis of these contigs reveals that D7S522 is located approximately 67 kb upstream of the caveolin-2 gene and that the caveolin-2 gene is located approximately 19 kb upstream of the caveolin-1 gene, providing for the first time a detailed genetic map of this region. Further sequence analysis reveals many interesting features of the caveolin genes; these include the intron-exon boundaries and several previously unrecognized CA repeats that lie within or in close proximity to the caveolin genes. The first and second exons of both caveolin genes are embedded within CpG islands. These results suggest that regulation of caveolin gene expression may be controlled, in part, by methylation of these CpG regions. In support of this notion, we show here that the CGs in the 5' promoter region of the caveolin-1 gene are functionally methylated in two human breast cancer cell lines (MCF7 and T-47D) that fail to express the caveolin-1 protein. In contrast, the same CGs in cultured normal human mammary epithelial cells (NHMECs) are non-methylated and these cells express high levels of the caveolin-1 protein. Comparison of the human locus with the same locus in the pufferfish Fugu rubripes reveals that the overall organization of the caveolin-1/-2 locus is conserved from pufferfish to man. In conclusion, our current studies provide a systematic basis for diagnostically evaluating the potential deletion, mutation, or methylation of the caveolin genes in a variety of human tumors.

Cyclin D- and E-dependent kinases and the p57(KIP2) inhibitor: cooperative interactions in vivo

This study examines in vivo the role and functional interrelationships of components regulating exit from the G1 resting phase into the DNA synthetic (S) phase of the cell cycle. Our approach made use of several key experimental attributes of the developing mouse lens, namely its strong dependence on pRb in maintenance of the postmitotic state, the down-regulation of cyclins D and E and up-regulation of the p57(KIP2) inhibitor in the postmitotic lens fiber cell compartment, and the ability to target transgene expression to this compartment. These attributes provide an ideal in vivo context in which to examine the consequences of forced cyclin expression and/or of loss of p57(KIP2) inhibitor function in a cellular compartment that permits an accurate quantitation of cellular proliferation and apoptosis rates in situ. Here, we demonstrate that, despite substantial overlap in cyclin transgene expression levels, D-type and E cyclins exhibited clear functional differences in promoting entry into S phase. In general, forced expression of the D-type cyclins was more efficient than cyclin E in driving lens fiber cells into S phase. In the case of cyclins D1 and D2, ectopic proliferation required their enhanced nuclear localization through CDK4 coexpression. High nuclear levels of cyclin E and CDK2, while not sufficient to promote efficient exit from G1, did act synergistically with ectopic cyclin D/CDK4. The functional differences between D-type and E cyclins was most evident in the p57(KIP2)-deficient lens wherein cyclin D overexpression induced a rate of proliferation equivalent to that of the pRb null lens, while overexpression of cyclin E did not increase the rate of proliferation over that induced by the loss of p57(KIP2) function. These in vivo analyses provide strong biological support for the prevailing view that the antecedent actions of cyclin D/CDK4 act cooperatively with cyclin E/CDK2 and antagonistically with p57(KIP2) to regulate the G1/S transition in a cell type highly dependent upon pRb.

Specific inhibitors of p38 mitogen-activated protein kinase block 3T3-L1 adipogenesis

SB203580 and SB202190, pyridinyl imidazoles that selectively inhibit p38 mitogen-activated protein (MAP) kinase, are widely utilized to assess the physiological roles of p38. Here, we demonstrate that treatment of 3T3-L1 fibroblasts with these p38 MAP kinase inhibitors prevents their differentiation into adipocytes as judged by an absence of lipid accumulation, a lack of expression of adipocyte-specific genes, and a fibroblastic morphological appearance. In 3T3-L1 fibroblasts and developing adipocytes, p38 is active. p38 activity decreases dramatically during later stages of differentiation. In accordance with the time course of p38 activity, p38 inhibitor treatment during only the early stages of differentiation is sufficient to block adipogenesis. In addition, we constructed a 3T3-L1 cell line harboring an inducible dominant negative p38 mutant. The induction of this dominant negative mutant of p38 prevents adipocyte differentiation. Thus, it is likely that the antiadipogenic activity of SB203580 and SB202190 is indeed due to inhibition of p38 MAP kinase. This study points out that CCAAT/enhancer-binding protein beta (C/EBPbeta), a transcription factor critical for the initial stages of 3T3-L1 adipogenesis, bears a consensus site for p38 phosphorylation and serves as a substrate for p38 MAP kinase in vitro. Although the induction of C/EBPbeta is not significantly altered in the presence of the p38 inhibitor, the amount of in vivo phosphorylated C/EBPbeta is reduced by SB203580. The transcriptional induction of PPARgamma, a gene whose expression is induced by C/EBPbeta, and a factor critically involved in terminal differentiation of adipocytes, is impaired in the presence of p38 inhibitors. Thus, transcription factors such as C/EBPbeta that promote adipocyte differentiation may be p38 targets during adipogenesis. Collectively, the data in this study suggest that p38 MAP kinase activity is important for proper 3T3-L1 differentiation.

Targeted downregulation of caveolin-1 is sufficient to drive cell transformation and hyperactivate the p42/44 MAP kinase cascade

Caveolin-1 is a principal component of caveolae membranes in vivo. Caveolin-1 mRNA and protein expression are lost or reduced during cell transformation by activated oncogenes. Interestingly, the human caveolin-1 gene is localized to a suspected tumor suppressor locus (7q31.1). However, it remains unknown whether downregulation of caveolin-1 is sufficient to mediate cell transformation or tumorigenicity. Here, we employ an antisense approach to derive stable NIH 3T3 cell lines that express dramatically reduced levels of caveolin-1 but contain normal amounts of caveolin-2. NIH 3T3 cells harboring antisense caveolin-1 exhibit anchorage-independent growth, form tumors in immunodeficient mice and show hyperactivation of the p42/44 MAP kinase cascade. Importantly, transformation induced by caveolin-1 downregulation is reversed when caveolin-1 protein levels are restored to normal by loss of the caveolin-1 antisense vector. In addition, we show that in normal NIH 3T3 cells, caveolin-1 expression levels are tightly regulated by specific growth factor stimuli and cell density. Our results suggest that upregulation of caveolin-1 may be important in mediating contact inhibition and negatively regulating the activation state of the p42/44 MAP kinase cascade.

Genes encoding human caveolin-1 and -2 are co-localized to the D7S522 locus (7q31.1), a known fragile site (FRA7G) that is frequently deleted in human cancers

The (CA)n microsatellite repeat marker D7S522 is located on human chromosome 7q31.1 and is frequently deleted in a variety of human cancers, including squamous cell carcinomas of the head and neck, prostate cancers, renal cell carcinomas, ovarian adenocarcinomas, colon carcinomas, and breast cancers. In addition, D7S522 spans FRA7G, a known common fragile site on human chromosome 7. Based on these studies, it has been proposed that an as yet unidentified tumor suppressor gene (or genes) is contained within or located in close proximity to this locus. However, the identity of the candidate tumor suppressor gene at the D7S522 locus remains unknown. Here, we show that the human genes encoding caveolins 1 and 2 are contained within the same human genomic BAC clones and co-localize to the q31.1-q31.2 region of human chromosome 7, as seen by FISH analysis. In addition, we determined the intron-exon boundaries of the human caveolin-1 and -2 genes. The human caveolin-1 gene contains three exons, while the human caveolin-2 gene contains two exons. Interestingly, the boundary of the last exon of the human caveolin-1 and caveolin-2 genes are analogous, suggesting that they arose through gene duplication at this locus. (CA)n microsatellite repeat marker analysis of these caveolin genomic clones indicates they contain the marker D7S522 (located at 7q31.1), but not other microsatellite repeat markers tested. The close proximity of caveolins 1 and 2 to the D7S522 locus was independently confirmed by using a panel of MIT/Whitehead human STS markers that are known to map in the neighborhood of the D7S522 locus. As it has been previously shown that caveolin 1 possesses transformation suppressor activity (Koleske, A.J., Baltimore, D. and M.P. Lisanti (1995) Proc. Natl. Acad. Sci. USA 92, 1381-1385; Engelman, J.A. et al. (1997) J. Biol. Chem. 272, 16374-16381), we propose that the caveolin-1 gene may represent the candidate tumor suppressor gene at the D7S522 locus on human chromosome 7q31.1.

Mutational analysis of caveolin-induced vesicle formation. Expression of caveolin-1 recruits caveolin-2 to caveolae membranes

Caveolae are vesicular organelles with a characteristic uniform diameter in the range of 50-100 nm. Although recombinant expression of caveolin-1 is sufficient to drive caveolae formation, it remains unknown what controls the uniform diameter of these organelles. One hypothesis is that specific caveolin-caveolin interactions regulate the size of caveolae, as caveolin-1 undergoes two stages of self-oligomerization. To test this hypothesis directly, we have created two caveolin-1 deletion mutants that lack regions of caveolin-1 that are involved in directing the self-assembly of caveolin-1 oligomers. More specifically, Cav-1 delta61-100 lacks a region of the N-terminal domain that directs the formation of high molecular mass caveolin-1 homo-oligomers, while Cav-1 deltaC lacks a complete C-terminal domain that is required to allow caveolin homo-oligomers to interact with each other, forming a caveolin network. It is important to note that these two mutants retain an intact transmembrane domain. Our current results show that although Cav-1 delta61-100 and Cav-1 deltaC are competent to drive vesicle formation, these vesicles vary widely in their size and shape with diameters up to 500-1000 nm. In addition, caveolin-induced vesicle formation appears to be isoform-specific. Recombinant expression of caveolin-2 under the same conditions failed to drive the formation of vesicles, while caveolin-3 expression yielded caveolae-sized vesicles. These results are consistent with the previous observation that in transformed NIH 3T3 cells that lack caveolin-1 expression, but continue to express caveolin-2, no morphologically distinguishable caveolae are observed. In addition, as caveolin-2 alone exists mainly as a monomer or homo-dimer, while caveolins 1 and 3 exist as high molecular mass homo-oligomers, our results are consistent with the idea that the formation of high molecular mass oligomers of caveolin are required to regulate the formation of uniform caveolae-sized vesicles. In direct support of this notion, regulated induction of caveolin-1 expression in transformed NIH 3T3 cells was sufficient to recruit caveolin-2 to caveolae membranes. The ability of caveolin-1 to recruit caveolin-2 most likely occurs through a direct interaction between caveolins 1 and 2, as caveolins 1 and 2 are normally co-expressed and interact with each other to form high molecular mass hetero-oligomers containing both caveolins 1 and 2.

Expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion neurons: caveolin-2 is up-regulated in response to cell injury

Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicular trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expression, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA species are detectable in the brain by Northern blot analyses or in neuroblastoma cell lines. However, it remains unknown whether caveolins are expressed within neuronal cells. Here we demonstrate the expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regulated early in the differentiation program and then rapidly down-regulated. Interestingly, caveolin-2 is up-regulated in response to the mechanical injury of differentiated PC12 cells; up-regulation of caveolin-2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed along the entire cell surface of DRG neurons, including high levels on growth cones. These findings demonstrate that neuronal cells express caveolins.

Reciprocal regulation of neu tyrosine kinase activity and caveolin-1 protein expression in vitro and in vivo. Implications for human breast cancer

Neu (c-erbB2) is a proto-oncogene product that encodes an epidermal growth factor-like receptor tyrosine kinase. Amplification of wild-type c-Neu and mutational activation of Neu (Neu T) have been implicated in oncogenic transformation of cultured fibroblasts and mammary tumorigenesis in vivo. Here, we examine the relationship between Neu tyrosine kinase activity and caveolin-1 protein expression in vitro and in vivo. Recent studies have suggested that caveolins may function as negative regulators of signal transduction. Our current results show that mutational activation of c-Neu down-regulates caveolin-1 protein expression, but not caveolin-2, in cultured NIH 3T3 and Rat 1 cells. Conversely, recombinant overexpression of caveolin-1 blocks Neu-mediated signal transduction in vivo. These results suggest a reciprocal relationship between c-Neu tyrosine kinase activity and caveolin-1 protein expression. We next analyzed a variety of caveolin-1 deletion mutants to map this caveolin-1-dependent inhibitory activity to a given region of the caveolin-1 molecule. Results from this mutational analysis show that this functional in vivo inhibitory activity is contained within caveolin-1 residues 32-95. In accordance with these in vivo studies, a 20-amino acid peptide derived from this region (the caveolin-1 scaffolding domain) was sufficient to inhibit Neu autophosphorylation in an in vitro kinase assay. To further confirm or refute the relevance of our findings in vivo, we next examined the expression levels of caveolin-1 in mammary tumors derived from c-Neu transgenic mice. Our results indicate that dramatic reduction of caveolin-1 expression occurs in mammary tumors derived from c-Neu-expressing transgenic mice and other transgenic mice expressing downstream effectors of Neu-mediated signal transduction, such as Src and Ras. Taken together, our data suggest that a novel form of reciprocal negative regulation exists between c-Neu and caveolin-1.

Crowded little caves: structure and function of caveolae

Caveolae are small vesicular invaginations of the cell membrane. It is within this organelle that cells perform transcytosis, potocytosis and signal transduction. These "little caves" are composed of a mixture of lipids and proteins unlike those found in the plasma membrane proper. The chief structural proteins of caveolae are caveolins. To date, three caveolins (Cav-1, -2 and -3) with unique tissue distributions have been identified. Caveolins form a scaffold onto which many signalling molecules can assemble, to generate pre-assembled signalling complexes. In addition to concentrating these signal transducers within a distinct region of the plasma membrane, caveolin binding may functionally regulate the activation state of caveolae-associated signalling molecules.

Chromosomal localization, genomic organization, and developmental expression of the murine caveolin gene family (Cav-1, -2, and -3). Cav-1 and Cav-2 genes map to a known tumor suppressor locus (6-A2/7q31)

Caveolins (Cav-1, -2, and -3) are a gene family of cytoplasmic membrane-anchored scaffolding proteins that: (i) help to sculpt caveolae membranes from the plasma membrane proper; and (ii) participate in the sequestration of inactive signaling molecules. In the adult, caveolin-1 and -2 are co-expressed and are most abundant in type I pneumocytes, endothelia, fibroblastic cells and adipocytes, while the expression of caveolin-3 is restricted to striated muscle cells. However, little is known regarding the genomic organization and developmental expression of the caveolin gene family. Here, using the mouse as a model system, we examine the chromosomal localization, the detailed intron-exon organization, and developmental expression pattern of the caveolin gene family. cDNAs encoding caveolin-1, -2, and -3 were used as probes to isolate murine genomic clones containing these genes. Fluorescence in situ hybridization (FISH) analysis using these genomic clones as probes reveals that all three caveolin genes are localized to murine chromosome 6. Specifically, caveolin-1 and -2 co-localize to chromosomal region 6-A2, while caveolin-3 is located within the chromosomal region 6-E1. Searches of the NCBI Human/Mouse Homology map indicate that murine region 6-A2 corresponds to human chromosome 7q31. As this region (6-A2/7q31) is the site of an as yet unidentified tumor suppressor gene(s), our mapping studies clearly define caveolin-1 and caveolin-2 as candidate genes that may be deleted at these loci. All three caveolin genes show similar intron-exon organization, with the last exon of each gene encoding the bulk of the known caveolin functional domains. The boundary position of the last exon is essentially identical in all three caveolin genes, suggesting that they may have arisen through gene duplication events. Developmentally, all three caveolins were expressed late during mouse embryogenesis as assessed by Northern and Western blot analysis. We examined the localization of the caveolin proteins in sections of day 16 mouse embryos using a well-characterized panel of antibody probes. Caveolin-1 and -2 were most abundantly expressed in the developing lung parenchyma, while caveolin-3 was most abundantly expressed in developing tissues that consist primarily of skeletal muscle cells. As the expression of all three caveolins in the adult is highest in terminally differentiated cell types, this is consistent with the idea that caveolins may be viewed as late markers of differentiation during embryogenesis.

Caveolin-mediated regulation of signaling along the p42/44 MAP kinase cascade in vivo. A role for the caveolin-scaffolding domain

The p42/44 mitogen-activated protein (MAP)-kinase cascade is a well-established signal transduction pathway that is initiated at the cell surface and terminates within the nucleus. More specifically, receptor tyrosine kinases can indirectly activate Raf, which in turn leads to activation of MEK and ERK and ultimately phosphorylation of Elk, a nuclear transcription factor. Recent reports have suggested that some members of p42/44 MAP kinase cascade can be sequestered within plasmalemmal caveolae in vivo. For example, morphological studies have directly shown that ERK-1/2 is concentrated in plasma membrane caveolae in vivo using immunoelectron microscopy. In addition, constitutive activation of the p42/44 MAP kinase cascade is sufficient to reversibly down-regulate caveolin-1 mRNA and protein expression. However, the functional relationship between the p42/44 MAP kinase cascade and caveolins remains unknown. Here, we examine the in vivo role of caveolins in regulating signaling along the MAP kinase cascade. We find that co-expression with caveolin 1 dramatically inhibits signaling from EGF-R, Raf, MEK-1 and ERK-2 to the nucleus. Using a variety of caveolin-1 deletion mutants, we mapped this in vivo inhibitory activity to caveolin-1 residues 32-95. Peptides derived from this region of caveolin 1 also inhibit the in vitro kinase activity of purified MEK-1 and ERK-2. Thus, we show here that caveolin-1 expression can inhibit signal transduction from the p42/44 MAP kinase cascade both in vitro and in vivo. Taken together with previous data, our results also suggest that a novel form of reciprocal negative regulation exists between p42/44 MAP kinase activation and caveolin-1 protein expression, i.e. up-regulation of caveolin-1 protein expression down-modulates p42/44 MAP kinase activity (this report) and up-regulation of p42/44 MAP kinase activity down-regulates caveolin-1 mRNA and protein expression.

Cell-type and tissue-specific expression of caveolin-2. Caveolins 1 and 2 co-localize and form a stable hetero-oligomeric complex in vivo

Caveolae are microdomains of the plasma membrane that have been implicated in organizing and compartmentalizing signal transducing molecules. Caveolin, a 21-24-kDa integral membrane protein, is a principal structural component of caveolae membrane in vivo. Recently, we and other laboratories have identified a family of caveolin-related proteins; caveolin has been re-termed caveolin-1. Here, we examine the cell-type and tissue-specific expression of caveolin-2. For this purpose, we generated a novel mono-specific monoclonal antibody probe that recognizes only caveolin-2, but not caveolins-1 and -3. A survey of cell and tissue types demonstrates that the caveolin-2 protein is most abundantly expressed in endothelial cells, smooth muscle cells, skeletal myoblasts (L6, BC3H1, C2C12), fibroblasts, and 3T3-L1 cells differentiated to adipocytes. This pattern of caveolin-2 protein expression most closely resembles the cellular distribution of caveolin-1. In line with these observations, co-immunoprecipitation experiments with mono-specific antibodies directed against either caveolin-1 or caveolin-2 directly show that these molecules form a stable hetero-oligomeric complex. The in vivo relevance of this complex was further revealed by dual-labeling studies employing confocal laser scanning fluorescence microscopy. Our results indicate that caveolins 1 and 2 are strictly co-localized within the plasma membrane and other internal cellular membranes. Ultrastructurally, this pattern of caveolin-2 localization corresponds to caveolae membranes as seen by immunoelectron microscopy. Despite this strict co-localization, it appears that regulation of caveolin-2 expression occurs independently of the expression of either caveolin-1 or caveolin-3 as observed using two different model cell systems. Although caveolin-1 expression is down-regulated in response to oncogenic transformation of NIH 3T3 cells, caveolin-2 protein levels remain unchanged. Also, caveolin-2 protein levels remain unchanged during the differentiation of C2C12 cells from myoblasts to myotubes, while caveolin-3 levels are dramatically induced by this process. These results suggest that expression levels of caveolins 1, 2, and 3 can be independently up-regulated or down-regulated in response to a variety of distinct cellular cues.

Recombinant expression of caveolin-1 in oncogenically transformed cells abrogates anchorage-independent growth

Caveolae are plasma membrane-attached vesicular organelles. Caveolin-1, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes in vivo. Both caveolae and caveolin are most abundantly expressed in terminally differentiated cells: adipocytes, endothelial cells, and muscle cells. Conversely, caveolin-1 mRNA and protein expression are lost or reduced during cell transformation by activated oncogenes such as v-abl and H-ras (G12V); caveolae are absent from these cell lines. However, its remains unknown whether down-regulation of caveolin-1 protein and caveolae organelles contributes to their transformed phenotype. Here, we have expressed caveolin-1 in oncogenically transformed cells under the control of an inducible-expression system. Regulated induction of caveolin-1 expression was monitored by Western blot analysis and immunofluorescence microscopy. Our results indicate that caveolin-1 protein is expressed well using this system and correctly localizes to the plasma membrane. Induction of caveolin-1 expression in v-Abl-transformed and H-Ras (G12V)-transformed NIH 3T3 cells abrogated the anchorage-independent growth of these cells in soft agar and resulted in the de novo formation of caveolae as seen by transmission electron microscopy. Consistent with its antagonism of Ras-mediated cell transformation, caveolin-1 expression dramatically inhibited both Ras/MAPK-mediated and basal transcriptional activation of a mitogen-sensitive promoter. Using an established system to detect apoptotic cell death, it appears that the effects of caveolin-1 may, in part, be attributed to its ability to initiate apoptosis in rapidly dividing cells. In addition, we find that caveolin-1 expression levels are reversibly down-regulated by two distinct oncogenic stimuli. Taken together, our results indicate that down-regulation of caveolin-1 expression and caveolae organelles may be critical to maintaining the transformed phenotype in certain cell populations.

Multistrain outbreak of chancroid in San Francisco, 1989-1991

Restriction fragment length polymorphism (RFLP) and plasmid analyses were used to evaluate an outbreak of Haemophilus ducreyi in San Francisco. Fifty-four cases of culture-confirmed chancroid occurred between May 1989 and May 1991. Of these, 46 (96%) were in men and 35 (65%) were in blacks; the median age of patients was 34 years. Among the 32 isolates submitted for RFLP and plasmid analyses, six different HindIII RFLP patterns were identified. Two RFLP types were found in patients who had recently traveled to Los Angeles, Korea, or El Salvador. Four RFLP types appeared to be acquired locally and were more common among blacks (P = .002), in patients with a history of a sexually transmitted disease (P = .01), and in those who used drugs or exchanged drugs or money for sex (P = .08). The use of RFLP analysis confirmed that this outbreak was associated with multiple strains of H. ducreyi and allowed for the identification of risk factors for locally acquired chancroid.

Confirmatory assay increases specificity of the chlamydiazyme test for Chlamydia trachomatis infection of the cervix

Enzyme immunoassays for the detection of chlamydial antigens are commonly used to diagnose Chlamydia trachomatis infection. As is true for all nonculture methods, the specificities of these tests are a concern. A confirmatory blocking assay (Abbott Laboratories, North Chicago, Ill.) was evaluated at four sexually transmitted disease test sites. This assay is designed to confirm true-positive Chlamydiazyme (CZ) specimens and to identify false-positive CZ reactions caused by cross-reacting bacteria. Cervical specimens were collected from 2,891 women. Chlamydia prevalence by tissue culture (TC) was 9.2% (266 of 2,891 specimens). Compared with TC, the sensitivity and specificity of CZ were 78.9% (210 of 266 specimens) and 98.2% (2,577 of 2,625 specimens), respectively. There were 48 CZ false-positive reactions. The direct fluorescent-antibody test (DFA) was positive for 31 of 48 false-positive reactions, indicating culture misses. Thus, when the standard was both TC and DFA, CZ sensitivity was 81.1% and CZ specificity was 99.3%. Of the 17 CZ-positive patients who were negative by both TC and DFA, 3 were negative on repeat CZ and 11 of 14 were identified as false positive by the confirmatory assay. The confirmatory test was positive for CZ-positive women who were positive by TC or DFA. Use of the confirmatory test, which increased the specificity to 99.9%, would increase confidence in positive CZ results and make the test more useful for screening populations with a low prevalence of C. trachomatis infection.