Characterization of Lysophospholipase D Activity in Mammalian Cell Membranes

Lysophosphatidic acid (LPA) is a lipid mediator that binds to G-protein-coupled receptors, eliciting a wide variety of responses in mammalian cells. Lyso-phospholipids generated via phospholipase A2 (PLA2) can be converted to LPA by a lysophospholipase D (lyso-PLD). Secreted lyso-PLDs have been studied in more detail than membrane-localized lyso-PLDs. This study utilized in vitro enzyme assays with fluorescent substrates to examine LPA generation in membranes from multiple mammalian cell lines (PC12, rat pheochromocytoma; A7r5, rat vascular smooth muscle; Rat-1, rat fibroblast; PC-3, human prostate carcinoma; and SKOV-3 and OVCAR-3, human ovarian carcinoma). The results show that membranes contain a lyso-PLD activity that generates LPA from a fluorescent alkyl-lyso-phosphatidylcholine, as well as from naturally occurring acyl-linked lysophospholipids. Membrane lyso-PLD and PLD activities were distinguished by multiple criteria, including lack of effect of PLD2 over-expression on lyso-PLD activity and differential sensitivities to vanadate (PLD inhibitor) and iodate (lyso-PLD inhibitor). Based on several lines of evidence, including siRNA knockdown, membrane lyso-PLD is distinct from autotaxin, a secreted lyso-PLD. PC-3 cells express GDE4 and GDE7, recently described lyso-PLDs that localize to membranes. These findings demonstrate that membrane-associated lyso-D activity, expressed by multiple mammalian cell lines, can contribute to LPA production.

Effects of lysophosphatidic acid on calpain-mediated proteolysis of focal adhesion kinase in human prostate cancer cells

BACKGROUND

Calcium-mediated proteolysis plays an important role in cell migration. Lysophosphatidic acid (LPA), a lipid mediator present in serum, enhances migration of carcinoma cells. The effects of LPA on calpain-mediated proteolysis were, therefore, examined in PC-3, a human prostate cancer cell line.

METHODS

Cultured PC-3 cells were used in studies utilizing pharmacologic interventions, immunoblotting, and confocal immunolocalization.

RESULTS

Focal adhesion kinase (FAK), a tyrosine kinase involved in cell adhesion, is rapidly proteolyzed in serum-starved PC-3 cells exposed to the calcium ionophore, ionomycin; Nck, p130CAS, PKCα, and Ras-GAP are also degraded. Thapsigargin, which causes more moderate increases in intracellular calcium, induces partial proteolysis of these proteins. Calpain inhibitors block the proteolytic responses to ionomycin and thapsigargin. Ionomycin does not induce proteolysis in cells maintained in serum, suggesting a protective role for growth factors contained in serum. LPA causes minor FAK proteolysis when added alone, but protects against ionomycin-induced proteolysis in a time-dependent manner. LPA also protects against the cell detachment that eventually follows ionomycin treatment. The response to LPA is blocked by an LPA receptor antagonist. A similar effect of LPA is observed in ionomycin-treated Rat-1 fibroblasts. In PC-3 cells, the protective effects of LPA and serum are correlated with phosphorylation and redistribution of paxillin, suggesting roles for phosphorylation-mediated protein-protein interactions.

CONCLUSIONS

The complex effects of LPA on calpain-mediated proteolysis of FAK and other adhesion proteins are likely to play a role in the ability of LPA to promote attachment, migration, and survival of prostate cancer cells.

Molecular diagnostics of melanoma fine-needle aspirates: a cytology-histology correlation study

Patients with advanced-stage melanoma harboring a BRAF mutation are candidates for BRAF inhibition as a therapeutic strategy. The use of fine-needle aspiration (FNA) to diagnose metastatic melanoma is increasing. Studies examining the predictive value of BRAF mutation analysis on melanoma FNAs via correlation with follow-up excision findings are lacking. We examined 37 consecutive FNA cases of metastatic melanoma in which the aspirated lesion was subsequently excised. DNA was purified from Diff-Quik-stained FNA smears and tissue blocks from corresponding excisions in parallel. BRAF mutation status was successfully obtained from both specimen types in 34 (92%) of 37 cases. BRAF mutations were detected in 12 (35%) of 34 cases-11 V600E and 1 V600K. Results of BRAF mutational analysis were concordant in all 34 FNA smear/tissue excision pairs. Thus, melanoma FNA for molecular diagnostics represents a rapid, minimally invasive, and effective management strategy in this era of precision medicine.

Ancillary techniques on direct-smear aspirate slides: a significant evolution for cytopathology techniques

Numerous cytologic techniques aimed at effectively acquiring patient material for molecular testing have been proposed. Such techniques are becoming ever more important in an age of personalized medicine. In this commentary, the authors explored some more commonly proposed techniques to aid in the molecular testing of cytologic specimens. These techniques include the use of cell blocks, direct cytologic smears, filter paper storage, frozen samples, and enriched cellular techniques such as ThinPrep and cytospin preparations. Direct-smeared slides demonstrate excellent preservation of DNA, are easy to prepare, and are amenable to immediate adequacy at the time of the fine-needle aspiration (FNA) procedure as well as effective subsequent tumor purity estimation. Cell block methods cannot be assessed at the time of FNA and often demonstrate insufficiency, whereas filter paper and frozen techniques do not allow for the direct assessment of the presence and purity of tumor cells in the sample. Direct-smeared slides are emerging as the most effective preparation and storage medium of cytologic material to be used for molecular testing. Their cost-effectiveness, ease of use, and reliability have cemented them as the optimal solution for cytopathologists to fulfill the role of providing advanced molecular testing on patient samples.

Ovarian steroid cell tumor with biallelic adenomatous polyposis coli inactivation in a patient with familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant cancer predisposition syndrome that accounts for approximately 0.5-1% of all colorectal cancer cases. It is caused by germline mutations in the gene encoding the adenomatous polyposis coli (APC) tumor suppressor. Somatic APC inactivation due to mutation or loss of heterozygosity (LOH) promotes the development of adenomatous polyps by stabilizing the transcriptional coactivator β-catenin. Although colorectal cancer is by far the most common malignancy seen in FAP patients, the widespread use of prophylactic colectomy in these patients has increased the clinical importance of extracolonic tumors that are part of the neoplastic spectrum in FAP. Many of these tumors exhibit LOH or somatic APC mutation, strongly supporting a causative role of APC inactivation in their pathogenesis. Here we describe a 47-year-old female FAP patient with clinical manifestations of virilization who was found to have an ovarian steroid cell tumor, a rare neoplasm not known to be associated with FAP. Immunohistochemical analysis of the ovarian tumor demonstrated strong nuclear β-catenin staining consistent with somatic APC inactivation, and molecular analysis confirmed biallelic APC inactivation in the tumor. Our findings provide the first evidence that ovarian steroid cell tumors may be an extracolonic manifestation of FAP and implicate β-catenin activation as an oncogenic mechanism in ovarian steroid cell tumorigenesis.

The application of molecular diagnostic studies interrogating EGFR and KRAS mutations to stained cytologic smears of lung carcinoma

EGFR and KRAS mutation analyses are of increasing importance for guiding the treatment of non-small cell lung carcinomas. Insufficient cellularity of cell blocks can represent an impediment to the performance of these tests. We investigated the usefulness of cytologic direct smears as an alternative specimen source for mutation testing. Tumor cell-enriched areas from freshly prepared and archived rapid Romanowsky-stained direct smears in 33 cases of lung carcinoma were microdissected for DNA isolation and evaluated for EGFR and KRAS mutations. EGFR mutations were detected in 3 adenocarcinomas; 2 tumors had the L858R substitution and 1 an exon 19 deletion. KRAS mutations affecting codon 12, 13, or 61 were detected in 11 cases (8 adenocarcinomas and 3 non-small cell carcinomas). EGFR and KRAS mutations were mutually exclusive. Hence, archived and freshly prepared direct smears represent a robust and valuable specimen source for molecular studies, especially when cell blocks exhibit insufficient cellularity.

Group consensus review minimizes the diagnosis of "follicular lesion of undetermined significance" and improves cytohistologic concordance

We conducted a group consensus review of thyroid aspirates that were previously interpreted as "atypia of undetermined significance/follicular lesion of undetermined significance" (AUS/FLUS) and followed by surgical interventions. The study aimed to investigate if consensus review would minimize the diagnosis of AUS/FLUS with an optimal interobserver agreement and also promote a better cytohistologic concordance. A group of reviewers who were blinded to the corresponding histologic findings simultaneously evaluated a total of 50 aspirates at a multiheaded light microscope. Using the Bethesda System for Reporting Thyroid Cytopathology as a guideline, a consensus interpretation was reached upon review of each aspirate. Interobserver agreement was calculated and recorded. The cytohistologic correlation was then performed between the consensus interpretation and the corresponding histologic diagnosis. The consensus review reclassified 26 (52%) aspirates as non-neoplasia/benign, 10 (20%) as follicular neoplasm/suspicious for a follicular neoplasm, 1 (2%) as papillary thyroid carcinoma, and 2 (4%) as nondiagnostic. Eleven (22%) aspirates remained AUS/FLUS. The interobserver agreement across the five diagnostic categories ranged from 71.6% to 100% with an average level of 88.8%. Cytohistologic concordance was achieved in 24 of 26 (92.3%) and 9 of 11 (81.8%) aspirates that were reclassified as non-neoplasia/benign and neoplasia/malignancy, respectively. A diagnostic accuracy of 89.2% (33/37) was obtained in reclassified cases. In conclusion, the group consensus review minimized AUS/FLUS, offered an optimal level of interobserver agreement, and most importantly, promoted excellent cytohistologic concordance in reclassified cases and, therefore, could play a substantial role in the future in reducing reaspiration and/or unnecessary surgeries.

Utility of PAX8 and PAX2 immunohistochemistry in the identification of renal cell carcinoma in diagnostic cytology

The diagnosis of metastatic renal cell carcinoma (RCC) in cytology specimens may be difficult to confirm on the basis of cytomorphology alone. Often, immunohistochemistry serves as an important adjunct in confirming this diagnosis. Recently, PAX2 was shown to be useful in this regard. In this study, we sought to compare the utility of PAX8 to that of PAX2 immunohistochemistry in the diagnosis of RCC in cytology specimens. First, we verified the performance of PAX8 immunohistochemistry on a tissue microarray (TMA) composed of 54 cases of RCC; PAX8 immunoreactivity was seen in at least 10% of the tumor cells in all cases. Next, we applied PAX8 immunohistochemistry to cell block sections prepared from 24 cases of RCC, obtained from fine-needle aspirates and effusion specimens. PAX2 immunohistochemistry was performed for comparison. Immunopositivity was defined as the presence of nuclear staining in at least 10% of tumor cell nuclei. Immunoreactivity for PAX8 and PAX2 was seen in 21 (88%) and 20 (83%) of the 24 cases, respectively. The presence of either PAX8 or PAX2 immunostaining was present in 22 of 24 cases, thus showing a total sensitivity of 92%. Overall, the results indicate that PAX8 and PAX2 are diagnostically useful adjuncts in confirming the diagnosis of RCC in cytology specimens.

Retroperitoneal germ cell tumor diagnosed by endoscopic ultrasound-guided fine needle aspiration

Isolated extragonadal germ cell tumors can be primary in nature or metastatic from a burned out testicular cancer. Accurate diagnosis is critical as appropriate therapy can be highly curative. We present the case of an isolated extragonadal germ cell tumor in the retroperitoneum diagnosed by endoscopic ultrasound-guided fine needle aspiration. This case underscores the importance of considering germ cell tumors in the differential diagnosis of an unexplained retroperitoneal mass, particularly since immunophenotypic staining may be necessary to establish the diagnosis.

Correlation between hybrid capture II high-risk human papillomavirus DNA test chemiluminescence intensity from cervical samples with follow-up histologic results: a cytologic/histologic review of 367 cases

BACKGROUND

The Hybrid Capture II high-risk human papillomavirus (hrHPV) DNA test is a US Food and Drug Administration-approved nucleic acid hybridization assay using chemiluminescence for the semiquantitative detection of hrHPV in cervical samples. Patient samples and controls are used to calculate results as negative for hrHPV if <1.0, positive for hrHPV if >2.5, and "equivocal" if between 1.0 and 2.5.

METHODS

The authors reported on the cervical histologic results of 209 patients demonstrating "equivocal" results for hrHPV from SurePath (204 patients) or ThinPrep (5 patients) vials, and compared patients in this cohort with atypical squamous cells of undetermined significance (ASC-US) cytology on the index cervical Papanicolaou (Pap) test (Group 1; n = 148 patients) with a patient cohort demonstrating unequivocal positive hrHPV test results (Group 2; n = 148 patients). The chemiluminescence intensity of hrHPV tests from patients in Group 2 were correlated with the presence and severity of dysplasia on subsequent histologic results, and patients were thereby stratified for their subsequent risk of cervical intraepithelial neoplasia (CIN) types II/III.

RESULTS

Approximately 97% of hrHPV tests demonstrating "equivocal" results were found to be positive at the time of retesting, and 15% of biopsied cases demonstrated CIN II or III. Results of follow-up histology after an ASC-US diagnosis, expressed as a percentage of the biopsied cohort, were: CIN II/III: 16.5% in Group 1 and 22.4% in Group 2; CIN I: 27% in Group 1 and 23.5% in Group 2; and negative: 56.5% in Group 1 and 54.1% in Group 2. Chemiluminescence intensity did not appear to be correlated with the severity of dysplasia.

CONCLUSIONS

The percentage of high-grade CIN in the "equivocal" hrHPV cohort is highly significant and therefore the management of these patients should be similar to the unequivocally positive population. After an unequivocal positive hrHPV test, the hrHPV chemiluminescence intensity does not appear to further predict the rate of high-grade CIN.

Minimizing the diagnosis of "follicular lesion of undetermined significance" and identifying predictive features for neoplasia

We used proposed standard morphologic criteria as a guideline to conduct a 10-year retrospective review of thyroid fine-needle aspiration specimens that were originally interpreted as "follicular lesion of undetermined significance" and followed by surgical intervention. We sought to investigate whether the indeterminate diagnosis could be minimized by assessing various cytomorphologic features and identifying the features predictive of neoplasia. Using the standard morphologic criteria, we semi-quantitatively assessed a total of 24 cytomorphologic features in 123 aspirates and recorded an overall interpretation on completion of the review. Cyto-histologic correlation was evaluated and logistic regression model was performed to identify cytomorphologic features predictive of neoplasia. Although 32 of 123 aspirates remained in the indeterminate category, the retrospective review reclassified 64 aspirates as non-neoplasia and 27 aspirates as neoplasia. Histologic confirmation was achieved in 47 (73.4%) non-neoplastic and 15 (55.6%) neoplastic aspirates with a diagnostic accuracy of 68.1%. Furthermore, our analysis demonstrated that neoplasia is positively associated with the presence of syncytial tissue fragments, isolated microfollicles, follicles with scalloped borders, scant cytoplasm, irregular nuclear membranes, nuclear overlapping, coarse chromatin, and increased cellularity. On the contrary, the presence of honeycombing tissue fragments, background colloid, and histiocytes inversely correlated with neoplasia. Overall, using proposed standard morphological criteria can minimize the diagnosis of "follicular lesion of undetermined significance," and allow for more accurate cyto-histologic correlation, and thereby playing a substantial role in reducing unnecessary surgical intervention.

Effects of active and inactive phospholipase D2 on signal transduction, adhesion, migration, invasion, and metastasis in EL4 lymphoma cells

The phosphatidylcholine-using phospholipase D (PLD) isoform PLD2 is widely expressed in mammalian cells and is activated in response to a variety of promitogenic agonists. In this study, active and inactive hemagglutinin-tagged human PLD2 (HA-PLD2) constructs were stably expressed in an EL4 cell line lacking detectable endogenous PLD1 or PLD2. The overall goal of the study was to examine the roles of PLD2 in cellular signal transduction and cell phenotype. HA-PLD2 confers PLD activity that is activated by phorbol ester, ionomycin, and okadaic acid. Proliferation and Erk activation are unchanged in cells transfected with active PLD2; proliferation rate is decreased in cells expressing inactive PLD2. Basal tyrosine phosphorylation of focal adhesion kinase (FAK) is increased in cells expressing active PLD2, as is phosphorylation of Akt; inactive PLD2 has no effect. Expression of active PLD2 is associated with increased spreading and elongation of cells on tissue culture plastic, whereas inactive PLD2 inhibits cell spreading. Inactive PLD2 also inhibits cell adhesion, migration, and serum-induced invasion. Cells expressing active PLD2 form metastases in syngeneic mice, as do the parental cells; cells expressing inactive PLD2 form fewer metastases than parental cells. In summary, active PLD2 enhances FAK phosphorylation, Akt activation, and cell invasion in EL4 lymphoma cells, whereas inactive PLD2 exerts inhibitory effects on adhesion, migration, invasion, and tumor formation. Overall, expression of active PLD2 enhances processes favorable to lymphoma cell metastasis, whereas expression of inactive PLD2 inhibits metastasis.

Resolution of equivocal results with the Hybrid Capture II high-risk HPV DNA test: a cytologic/histologic review of 191 cases

INTRODUCTION

The Hybrid Capture II (HC II, Digene) high-risk human papilloma virus (HPV) (hrHPV) DNA test is an in vitro nucleic acid hybridization assay that uses enhanced chemiluminescence for the qualitative and semiquantitative detection of hrHPV in cervical samples. Patient samples are concomitantly tested with positive and negative DNA controls and results reported as positive or negative on the basis of a ratio of relative light units to a cutoff value derived from the positive control (RLU/CO). Samples with a ratio <1.0 RLU/CO are expressed as negative for hrHPV, samples with a ratio >2.5 RLU/CO are expressed as positive for hrHPV, and samples with a ratio between these numbers are submitted for retesting. These "equivocal" values are resulted as positive for hrHPV if either of 2 subsequent test values equals or exceeds 1.0 RLU/CO. Samples that show <1.0 RLU/CO after 2 repeat tests are resulted as negative for hrHPV.

METHODS

In this study, we evaluated all hrHPV test results over a 17-month period in our institution. Initial tests showing an equivocal result were analyzed for final retesting result, and for all corresponding and subsequent cytology and histology results. All hrHPV tests were conducted on SurePath (TriPath) or ThinPrep (Cytyc) cervical cytology specimens using the HC II hrHPV DNA test. Subsequent hrHPV tests also were correlated with incident and follow-up findings.

RESULTS

A total of 4792 hrHPV test results were evaluated. Of these, 191 (4%) showed equivocal initial results. When retested, 178 of the 191 samples (93%) resulted positive for hrHPV on first retest and an additional 8 resulted positive for hrHPV on the second retest, bringing the total positive tests to 186 out of 191 (97.4%). Five samples (2.6%) out of 191 were finally expressed as negative for hrHPV. Corresponding cytologic interpretations for the 191 specimens were as follows: NILM-30, atypical squamous cell of undetermined significance (ASC-US)-138, atypical squamous cells--cannot exclude HSIL-13 (ASC-H-13), LSIL-9, and high-grade squamous intraepithelial lesion (HSIL)-1. Follow-up histology was available for 60 of the 191 equivocal cases and showed cervical intraepithelial neoplasia (CIN) II or CIN III in 7 cases, CIN I in 13 cases, and negative or reactive changes in 40 cases.

CONCLUSIONS

On the basis of the results, repeat testing of equivocal specimens might not be necessary as these specimens are overwhelmingly found to be positive for hrHPV. Additionally, hrHPV tests falling in the equivocal range should be considered as definite positive tests, as follow-up results in this cohort demonstrate that significant histologic abnormalities are associated with 10.5% of these cases (20/191), and with 33% of those biopsied (20/60) cases.

Green bone

OBJECTIVE

To describe the unusual finding of yellow-green-colored bone during routine orbital surgery, to detail its investigation, and to demonstrate its benign nature.

METHODS

When green bone was found, specimens were sent for light and fluorescent microscopy, ultraviolet photography, and spectrophotometry.

RESULTS

Yellow-green bone was encountered in 3 patients during orbital tumor excision or orbital fracture repair procedures. The only common cause was prior use of tetracycline during adolescence. All patients had healthy white dentition. In all cases, absence of neoplasia was demonstrated histologically. The bone fluoresced with a bright yellow-green color when exposed to 365-nm ultraviolet light. Histologic analysis demonstrated fluorescence located near the haversian canals. Spectrophotometry revealed absorption at 4 wavelengths specific to tetracycline: 230, 275, 380, and 440 nm.

CONCLUSIONS

Fixation of tetracycline and ensuing fluorescence occurs mostly in areas of new bone growth and mineralization. This happens during childhood but also with bone remodeling associated with tumors or fractures. Once mineralized, teeth should therefore not be affected if tetracycline exposure occurs after ages 8 to 10 years. This paucity of external clues can lead to the surprising but innocuous surgical finding of green bone. Careful history and proper investigation can confirm its origin.

Postmortem Urine Immunoassay Showing False-Positive Phencyclidine Reactivity in a Case of Fatal Tramadol Overdose

This is a report of postmortem false-positive reactivity using an enzyme-multiplied urine phencyclidine (PCP) immunoassay (EMIT II+) due to a single-agent fatal tramadol overdose. An autopsy of a 42-year-old male who died alone at home revealed no identifiable lethal anatomic abnormalities, thus leading to toxicologic analysis. Femoral blood was obtained for drug testing by high-performance liquid chromatography (HPLC) and showed a tramadol level of 14.0 mg/L, 2 orders of magnitude greater than the therapeutic range (0.1 to 0.3 mg/L). Urine was also obtained and EMIT II+ immunoassay revealed positivity for PCP at 88 mAU/min. However, confirmatory testing by HPLC failed to identify PCP in either the urine or serum. To verify the suspicion that this was a false-positive PCP result, stock solutions of tramadol and its major metabolite (O-desmethyltramadol) at concentrations of 100 mg/L in 10% methanol/H2O were compared with a blank solution (10% methanol/H2O) for EMIT II+ PCP reactivity and demonstrated reactivities of 44 mAU/min and 27 mAU/min, respectively. While these individual results were below the cutoff reactivity for a positive EMIT II+ PCP result (ca. 85 mAU/min), they were much more reactive than the blank calibrator (set at 0 mAU/min). Therefore, we conclude that the immunoreactivity of tramadol and its metabolites in aggregate is responsible for the PCP immunoassay interference and false-positive result.

RasGRP1 confers the phorbol ester-sensitive phenotype to EL4 lymphoma cells

The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to the tumor promoter phorbol 12-myristate 13-acetate (PMA). In sensitive EL4 cells, PMA causes robust Erk mitogen-activated protein kinase activation that results in growth arrest. In resistant cells, PMA induces minimal Erk activation, without growth arrest. PMA stimulates IL-2 production in sensitive, but not resistant, cells. The role of RasGRP1, a PMA-activated guanine nucleotide exchange factor for Ras, in EL4 phenotype was examined. Endogenous RasGRP1 protein is expressed at much higher levels in sensitive than in resistant cells. PMA-induced Ras activation is observed in sensitive cells but not in resistant cells lacking Ras-GRP1. PMA induces down-regulation of RasGRP1 protein in sensitive cells but increases RasGRP1 in resistant cells. Transfection of RasGRP1 into resistant cells enhances PMA-induced Erk activation. In the reverse experiment, introduction of small interfering RNA (siRNA) for RasGRP1 suppresses PMA-induced Ras and Erk activations in sensitive cells. Sensitive cells incubated with siRNA for RasGRP1 exhibit the PMA-resistant phenotype, in that they are able to proliferate in the presence of PMA and do not secrete IL-2 when stimulated with PMA. These studies indicate that the PMA-sensitive phenotype, as previously defined for the EL4 cell line, is conferred by endogenous expression of RasGRP1 protein.

Aspirin resistance: moving forward with multiple definitions, different assays, and a clinical imperative

Many patients are treated with aspirin to prevent a serious vascular event, most notably myocardial infarction and stroke. A growing number of studies have been appearing in the literature that indicate a significant fraction of aspirin-treated patients may be resistant to the antiplatelet effects of the drug. Resistance to aspirin may be related to the concomitant ingestion of aspirin and nonsteroidal anti-inflammatory drugs, which impairs the aspirin effect, or to more complex situations, such as metabolic defects that diminish the therapeutic effect of aspirin. The incidence of aspirin resistance is unknown, but it may approach 20% to 30%. The diagnosis of aspirin resistance has been evaluated using multiple assays, and because there are multiple assays, this has resulted in multiple definitions for aspirin resistance. This review considers aspirin resistance at a time when there is confusion about the definition, and the clinical assay to best assess it, because there is a clinical imperative to know now which patients taking aspirin are not receiving a therapeutic effect.

The colon anion transporter, down-regulated in adenoma, induces growth suppression that is abrogated by E1A

The down-regulated in adenoma (DRA) gene is significantly down-regulated in adenomas and adenocarcinomas of the colon as well as in colon cancer cell lines. It is also mutated in the disease congenital chloride diarrhea, which is characterized by loss of chloride transport and diarrhea. We now show a second function for DRA relevant to colon tumorigenesis, i.e., growth suppression. Transfection of full-length DRA into various cell lines (DLD-1, HT-29, HCT-15, SW837, SW480, MCF-7, NIH3T3, CaSki, and HeLa) that lack endogenous DRA expression results in a reduced number of drug-resistant colonies compared with vector control, suggesting growth suppression by DRA. In addition, expression of DRA under the control of an inducible promoter reduced the growth rate of DLD-1 cells compared with cells not expressing DRA. The COOH-terminal cytoplasmic domain of DRA is required for growth suppression, but an in-frame deletion (DeltaVal317) that causes congenital chloride diarrhea and results in a loss of anion transport had no effect on growth suppression, indicating that anion transport and growth suppression are independent functions of DRA. One cell line, adenovirus-transformed HEK293, exhibited significant resistance to DRA-induced growth suppression, whereas the human papillomavirus-transformed cell lines, CaSki and HeLa, did not. E1A is an adenoviral protein required to transform HEK293 cells. DLD-1 cells that stably express 12S E1A are resistant to growth suppression by DRA, similar to HEK293 cells.

Expression of phospholipase D isoforms in mammalian cells

Two mammalian isoforms of phospholipase D, PLD1 and PLD2, have recently been characterized at the molecular level. Effects of physiologic agonists on PLD activity in intact cells, as characterized in earlier studies, have generally not been attributed to specific PLD isoforms. Recent work has established that expression of PLD1 and PLD2 varies within tissues and between cell lines. A single cell type can express one, both, or neither isoform, although most cells co-express PLD1 and PLD2. Lymphocytes often lack expression of one or both isoforms of PLD. Relative levels of PLD mRNA expression vary considerably between established cell lines. Expression of transcripts for both PLD1 and PLD2 can be regulated at the transcriptional level by growth and differentiation factors in cultured cells. Thus, it is apparent that the known mammalian PLD isoforms are subject to regulation at the transcriptional level. The available data do not conclusively establish whether PLD1 and PLD2 are the only isoforms responsible for agonist-mediated PLD activation. Further studies of the regulation of expression of PLD isoforms should provide insight into the roles of PLD1 and PLD2 in physiologic responses, and may suggest whether additional forms of PLD remain to be characterized.

Synergistic effects of insulin and phorbol ester on mitogen-activated protein kinase in Rat-1 HIR cells

Regulation of the activity of the extracellular signal regulated kinase (ERK) mitogen-activated protein kinases was examined in Rat-1 HIR, a fibroblast cell line overexpressing the human insulin receptor. Insulin or phorbol ester induced partial activations of ERKs, while a combination of insulin and phorbol ester resulted in a synergistic activation. Preincubation with phorbol ester increased the subsequent response to insulin. Phorbol ester did not enhance tyrosine phosphorylation of the insulin receptor. Insulin did not enhance activation of phospholipase D in response to phorbol ester. Lysophosphatidic acid also acted synergistically with insulin to induce ERK activation. Lysophosphatidic acid alone had little effect on ERK, and did not activate phospholipase D. The combination of phorbol ester and insulin maintained tyrosine phosphorylation of focal adhesion kinase, while insulin alone decreased its tyrosine phosphorylation. Phorbol ester induced phosphorylation of She on serine/threonine, while insulin induced tyrosine phosphorylation of She and She-Grb2 binding. These results suggest that full activation of ERKs in fibroblasts can require the cooperation of at least two signaling pathways, one of which may result from a protein kinase C-dependent phosphorylation of effectors regulating ERK activation. In this manner, phorbol esters may enhance mitogenic signals initiated by growth factor receptors.