Confined migration induces heterochromatin formation and alters chromatin accessibility

During migration, cells often squeeze through small constrictions, requiring extensive deformation. We hypothesized that nuclear deformation associated with such confined migration could alter chromatin organization and function. By studying cells migrating through microfluidic devices that mimic interstitial spaces in vivo, we found that confined migration results in increased H3K9me3 and H3K27me3 heterochromatin marks that persist for days. This "confined migration-induced heterochromatin" (CMiH) was distinct from heterochromatin formation during migration initiation. Confined migration decreased chromatin accessibility at intergenic regions near centromeres and telomeres, suggesting heterochromatin spreading from existing sites. Consistent with the overall decrease in accessibility, global transcription was decreased during confined migration. Intriguingly, we also identified increased accessibility at promoter regions of genes linked to chromatin silencing, tumor invasion, and DNA damage response. Inhibiting CMiH reduced migration speed, suggesting that CMiH promotes confined migration. Together, our findings indicate that confined migration induces chromatin changes that regulate cell migration and other functions.

Abstract 3830: Chemical, molecular, and single cell analysis reveal chondroitin sulfate proteoglycan aberrancy in fibrolamellar carcinoma

The tumor microenvironment is a complex milieu relevant to the progression of cancer. A detailed analysis needs to be performed for each cancer type to identify relevant cell types and secreted factors promoting metastasis. Fibrolamellar carcinoma (FLC) is an aggressive liver cancer that predominantly afflicts adolescents and young adults who lack predisposing conditions, and patients with FLC are characterized by a heterozygous deletion on chromosome 19 that creates an oncogenic gene fusion, DNAJB1-PRKACA. The extracellular environment of FLC tumors is poorly characterized and may contribute to cancer progression, metastasis, and/or drug resistance. To bridge this knowledge gap, we performed experiments to assess pathways relevant to proteoglycans, a major component of the extracellular matrix. We first analyzed gene expression data from FLC and non-malignant liver tissue (n=27) to identify changes in pathways pertinent to glycosaminoglycan (GAG) biosynthesis. We then developed and implemented a novel chemical analytics method, utilizing custom molecular standards, to quantify the abundance of different types of GAGs in patient tumor samples by liquid chromatography with tandem mass spectrometry. We then measured the mRNA and protein levels of different GAG-associated proteins, followed by immunohistochemical confirmation. Finally, we performed the first single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) on FLC tumors to define the heterogeneous cellular landscape and to identify cell types likely responsible for producing the most dominant GAG-associated protein in FLC. We found that chondroitin sulfate (CS) but not heparan sulfate (HS) or hyaluronic acid (HA) biosynthesis genes are dramatically increased in FLC, especially the rate-limiting enzyme CS GalNAc transferase 1 (CSGALNACT1). We also determined that CS chains are significantly elevated in FLC. Further analysis showed that versican (VCAN) is the primary CS-associated protein in FLC, that CSGALNACT1 and VCAN are correlated with DNAJB1-PRKACA levels, and that VCAN is more highly expressed in FLC compared to almost all other cancer types. Finally, the single cell ATAC-seq analyses demonstrated for the first time the cellular heterogeneity of FLC and revealed that the VCAN locus is active in tumor epithelial cells but is most active in proliferating stellate cells. This study merges chemical, molecular, and single-cell analyses to uncover the marked elevation of chondroitin sulfate proteoglycans in FLC tumors. Our results suggest that VCAN may play a critical role in FLC tumor growth and/or metastasis. We also identified the presence of activated stellate cells in FLC tumors and suggest a role in propagating fibrosis. Future studies are required to identify whether and how attenuation of CS and/or VCAN mitigates proliferative and/or metastatic potential in FLC.

Citation Format: Adam Francisco, Jine Li, Alaa Farghili, Matt Kanke, Bo Shui, Wencheng Zhang, Paul Soloway, Zhangjie Wang, Lola Reid, Praveen Sethupathy. Chemical, molecular, and single cell analysis reveal chondroitin sulfate proteoglycan aberrancy in fibrolamellar carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3830.

Abstract 1460: Decoding the tumor biology of the orphan malignancy fibrolamellar carcinoma at single-cell resolution

The World Health Organization (WHO) recognized fibrolamellar carcinoma (FLC) in 2010 as a rare and aggressive form of liver cancer that predominately afflicts adolescents and young adults. There are currently no effective therapies. Surgical resection remains the only option to date, but it is not viable for patients who present with metastasis. Thus, there is an urgent need to identify therapeutic targets. The hallmark genetic lesion of FLC, occurring in >80% of patients, was recently identified to be a ~400kb heterozygous deletion on chromosome 19, leading to the oncogenic fusion protein DNAJB1-PRKACA (DP).

We recently used FLC primary tumors and matched non-malignant liver samples to map the chromatin activity landscape of FLC by chromatin run-on sequencing, or ChRO-seq, which is a state-of-the-art technology for quantifying nascent transcription and defining active regulatory elements across the genome. We identified nearly 7000 FLC-specific enhancers and ~150 “super-enhancers” (SEs) - dense clusters of highly active enhancers that mark nearby critical oncogenes. Despite these advances, a major limitation is the bulk tissue nature of the study - that is, these data reflect an average profile across numerous different cell types (hepatocytes, stellate cells, fibroblasts, macrophages, endothelial cells, etc.), and therefore it is not evident which enhancers and genes are active in which cell types. This represents a major knowledge gap. If we could learn the specific cell types in which FLC enhancers and genes are active, we could then study the functions of these genes in FLC with greater precision and develop more effective targeted therapeutics. I recently conducted single-cell Assay for Transposase Accessible Chromatin ATAC-seq (scATAC-seq) to bridge this knowledge gap. I identified eight clusters from FLC-Primary, FLC-Metastatic, and non-malignant liver (NML) samples. Dimensionality reduction reveals two FLC-Primary, and FLC-Metastatic derived clusters that exhibit an epithelial-like identity most closely related to NML-epithelial cells. Using this scATAC-seq dataset, I have deconvoluted and resolved the bulk resolution limitations of ChRO-seq signal. ScATAC-seq reveals ChRO-seq defined candidate genes are highly accessible in FLC-Primary and FLC-Metastatic transformed Epithelial Cells. I have also dissected ChRO-seq defined SE’s and detailed the proportion of active constituent enhancers within each cell type. Further analysis revealed cell-type-specific transcriptional networks. Together, these studies provide the first single-cell resolution understanding of the transcriptional network in FLC.

Citation Format: Alaa R. Farghli, Bo Shui, Seoyeon Lee, Paul R. Munn, Yutong Zhu, Paul Soloway, Praveen Sethupathy. Decoding the tumor biology of the orphan malignancy fibrolamellar carcinoma at single-cell resolution [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1460.

Approaching the single molecule. Interview by Kristie Nybo

Paul Soloway's development of single molecule approaches to study epigenetics caught our attention. Curious to know more, BioTechniques contacted him to find out about the ambition, character, and motivation that led to his success.

Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) controls activation of extracellular signal-regulated kinase (ERK) signaling in the striatum and long-term behavioral responses to cocaine

BACKGROUND

Ras-extracellular signal-regulated kinase (Ras-ERK) signaling is central to the molecular machinery underlying cognitive functions. In the striatum, ERK1/2 kinases are co-activated by glutamate and dopamine D1/5 receptors, but the mechanisms providing such signaling integration are still unknown. The Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a neuronal specific activator of Ras-ERK signaling, is a likely candidate for coupling these neurotransmitter signals to ERK kinases in the striatonigral medium spiny neurons (MSN) and for modulating behavioral responses to drug abuse such as cocaine.

METHODS

We used genetically modified mouse mutants for Ras-GRF1 as a source of primary MSN cultures and organotypic slices, to perform both immunoblot and immunofluorescence studies in response to glutamate and dopamine receptor agonists. Mice were also subjected to behavioral and immunohistochemical investigations upon treatment with cocaine.

RESULTS

Phosphorylation of ERK1/2 in response to glutamate, dopamine D1 agonist, or both stimuli simultaneously is impaired in Ras-GRF1-deficient striatal cells and organotypic slices of the striatonigral MSN compartment. Consistently, behavioral responses to cocaine are also affected in mice deficient for Ras-GRF1 or overexpressing it. Both locomotor sensitization and conditioned place preference are significantly attenuated in Ras-GRF1-deficient mice, whereas a robust facilitation is observed in overexpressing transgenic animals. Finally, we found corresponding changes in ERK1/2 activation and in accumulation of FosB/DeltaFosB, a well-characterized marker for long-term responses to cocaine, in MSN from these animals.

CONCLUSIONS

These results strongly implicate Ras-GRF1 in the integration of the two main neurotransmitter inputs to the striatum and in the maladaptive modulation of striatal networks in response to cocaine.

Tissue inhibitor of metalloproteinase-2(TIMP-2)-deficient mice display motor deficits

The degradation of the extracellular matrix is regulated by matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Matrix components of the basement membrane play critical roles in the development and maintenance of the neuromuscular junction (NMJ), yet almost nothing is known about the regulation of MMP and TIMP expression in either the pre- or postsynaptic compartments. Here, we demonstrate that TIMP-2 is expressed by both spinal motor neurons and skeletal muscle. To determine whether motor function is altered in the absence of TIMP-2, motor behavior was assessed using a battery of tests (e.g., RotaRod, balance beam, hindlimb extension, grip strength, loaded grid, and gait analysis). TIMP-2(-/-) mice fall off the RotaRod significantly faster than wild-type littermates. In addition, hindlimb extension is reduced and gait is both splayed and lengthened in TIMP-2(-/-) mice. Motor dysfunction is more pronounced during early postnatal development. A preliminary analysis revealed NMJ alterations in TIMP-2(-/-) mice. Juvenile TIMP-2(-/-) mice have increased nerve branching and acetylcholine receptor expression. Adult TIMP-2(-/-) endplates are enlarged and more complex. This suggests a role for TIMP-2 in NMJ sculpting during development. In contrast to the increased NMJ nerve branching, cerebellar Purkinje cells have decreased neurite outgrowth. Thus, the TIMP-2(-/-) motor phenotype is likely due to both peripheral and central defects. The tissue specificity of the nerve branching phenotype suggests the involvement of different MMPs and/or extracellular matrix molecules underlying the TIMP-2(-/-) motor phenotype.

Prepulse inhibition and fear-potentiated startle are altered in tissue inhibitor of metalloproteinase-2 (TIMP-2) knockout mice

The ability to discriminate between potential dangers and recall those stimuli is essential for survival. This emotional learning requires the involvement of higher brain structures, including the amygdala, hippocampus and related cortical structures. Long-term changes in synaptic transmission and structure are important for the establishment and consolidation of fear memory. The structural changes associated with this synaptic plasticity likely require alterations in the composition of the extracellular matrix (ECM). ECM integrity is maintained by the opposing action of matrix metalloproteinases (MMPs) and their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs). To date, no studies have examined the role of MMPs or TIMPs in conditioned fear. Here, we show that neither male nor female mice deficient in TIMP-2 (knockout) exhibit prepulse inhibition of the startle reflex, suggesting deficits in pre-attentional sensorimotor gating. In addition, knockout mice and mice expressing a mutant truncated TIMP-2 (knock-down) show deficits in fear-potentiated startle. This is the first report of a phenotype for the TIMP-2(-/-) mice and suggests that TIMP-2 may play a role in the synaptic plasticity underlying learning and memory.

Tumor cell traffic through the extracellular matrix is controlled by the membrane-anchored collagenase MT1-MMP

As cancer cells traverse collagen-rich extracellular matrix (ECM) barriers and intravasate, they adopt a fibroblast-like phenotype and engage undefined proteolytic cascades that mediate invasive activity. Herein, we find that fibroblasts and cancer cells express an indistinguishable pericellular collagenolytic activity that allows them to traverse the ECM. Using fibroblasts isolated from gene-targeted mice, a matrix metalloproteinase (MMP)–dependent activity is identified that drives invasion independently of plasminogen, the gelatinase A/TIMP-2 axis, gelatinase B, collagenase-3, collagenase-2, or stromelysin-1. In contrast, deleting or suppressing expression of the membrane-tethered MMP, MT1-MMP, in fibroblasts or tumor cells results in a loss of collagenolytic and invasive activity in vitro or in vivo. Thus, MT1-MMP serves as the major cell-associated proteinase necessary to confer normal or neoplastic cells with invasive activity.

Site-specific inductive and inhibitory activities of MMP-2 and MMP-3 orchestrate mammary gland branching morphogenesis

During puberty, mouse mammary epithelial ducts invade the stromal mammary fat pad in a wave of branching morphogenesis to form a complex ductal tree. Using pharmacologic and genetic approaches, we find that mammary gland branching morphogenesis requires transient matrix metalloproteinase (MMP) activity for invasion and branch point selection. MMP-2, but not MMP-9, facilitates terminal end bud invasion by inhibiting epithelial cell apoptosis at the start of puberty. Unexpectedly, MMP-2 also represses precocious lateral branching during mid-puberty. In contrast, MMP-3 induces secondary and tertiary lateral branching of ducts during mid-puberty and early pregnancy. Nevertheless, the mammary gland is able to develop lactational competence in MMP mutant mice. Thus, specific MMPs refine the mammary branching pattern by distinct mechanisms during mammary gland branching morphogenesis.

Sequence motifs of tissue inhibitor of metalloproteinases 2 (TIMP-2) determining progelatinase A (proMMP-2) binding and activation by membrane-type metalloproteinase 1 (MT1-MMP)

Fundamental cellular processes including angiogenesis and cell migration require a proteolytic cascade driven by interactions of membrane-type matrix metalloproteinase 1 (MT1-MMP) and progelatinase A (proMMP-2) that are dependent on the presence of tissue inhibitor of metalloproteinases 2 (TIMP-2). There are unique interactions between TIMP-2 and MT1-MMP, which we have previously defined, and here we identify TIMP-2 sequence motifs specific for proMMP-2 binding in the context of its activation by MT1-MMP. A TIMP-2 mutant encoding the C-terminal domain of TIMP-4 showed loss of proMMP-2 activation, indicating that the C-terminal domain of TIMP-2 is important in establishing the trimolecular complex between MT1-MMP, TIMP-2 and proMMP-2. This was confirmed by analysis of a TIMP-4 mutant encoding the C-terminal domain of TIMP-2, which formed a trimolecular complex and promoted proMMP-2 processing to the intermediate form. Mutants encoding TIMP-4 from Cys(1) to Leu(185) and partial tail sequence of TIMP-2 showed some gain of activating capability relative to TIMP-4. The identified residues were subsequently mutated in TIMP-2 (E(192)-D(193) to I(192)-Q(193)) and this inhibitor showed a significantly reduced ability to facilitate proMMP-2 processing by MT1-MMP. Furthermore, the tail-deletion mutant Delta(186-194)TIMP-2 was completely incapable of promoting proMMP-2 activation by MT1-MMP. Thus the C-terminal tail residues of TIMP-2 are important determinants for stable trimolecular complex formation between TIMP-2, proMMP-2 and MT1-MMP and play an important role in MT1-MMP-mediated processing to the intermediate and final active forms of MMP-2 at the cell surface.

Cellular activation of proMMP-13 by MT1-MMP depends on the C-terminal domain of MMP-13

Procollagenase-3 (proMMP-13) can be activated by soluble or cell associated membrane type matrix metalloproteinase 1 (MT1-MMP). In this study we show that the cell based activation of proMMP-13 by MT1-MMP was dependent on the C-terminal domain, as delta(249-451) proMMP-13, which lacks the haemopexin domain, and a chimaera from N-terminal MMP-13 and C-terminal MMP-19 (proMMP-13/19) were not processed by MT1-MMP expressing cells. Only the initial cleavage at Gly(35)-Ile(36) was dependent on MT1-MMP activity, as conversion to the active enzyme (Tyr(85) N-terminus) required a functional MMP-13 active site. Unlike proMMP-2 activation, this process was independent of tissue inhibitor of metalloproteinase-2 (TIMP-2) as MT1-MMP expressing cells from the TIMP-2-/- mouse efficiently activated proMMP-13.

Structural characterization of Rasgrf1 and a novel linked imprinted locus

Imprinted genes in mammals are expressed either from the maternally or the paternally inherited allele. Previously, a genome wide scan identified novel imprinted genes based on their association with differentially methylated regions (DMRs). One of the identified genes, Rasgrf1, showed paternal expression in neonatal brain and was located on mouse chromosome 9. This gene is associated with a DMR, located about 30 kb upstream of Rasgrf1 exon 1. In order to better understand and identify novel elements involved in the regulation of this gene we have isolated and characterized genomic clones coding for mouse and human Rasgrf1 and RASGRF1, respectively. The mouse gene consists of 26 exons spanning approximately 140 kb of genomic DNA while the human gene has 28 exons. The human gene has an additional 39 bp exon inserted between exons 13 and 14 and exon 18 is split in two separate exons in human. The major transcription start site of Rasgrf1, as identified by primer extension, is 1324 bp upstream of the ATG translation start codon. Finally, a genomic region upstream of exon 1, spanning 489 bp, was determined to possess the essential promoter activity for Rasgrf1 gene. A second gene, A19, located 10 kb upstream of the DMR has been characterized. A19 is mainly expressed in testis and at lower levels in neonatal and adult brain tissue. The A19 transcript is non-coding and expressed in mouse testis and brain. A19 is imprinted with expression occurring from just the paternal allele in brain.

Elevated matrix metalloprotease and angiostatin levels in integrin alpha 1 knockout mice cause reduced tumor vascularization

Integrin alpha1beta1 is a collagen receptor abundantly expressed on microvascular endothelial cells. As well as being the only collagen receptor able to activate the Ras/Shc/mitogen-activated protein kinase pathway promoting fibroblast cell proliferation, it also acts to inhibit collagen and metalloproteinase (MMP) synthesis. We have observed that in integrin alpha1-null mice synthesis of MMP7 and MMP9 was markedly increased compared with that of their wild-type counterparts. As MMP7 and MMP9 have been shown to generate angiostatin from circulating plasminogen, and angiostatin acts as a potent inhibitor of endothelial cell proliferation, we determined whether tumor vascularization was altered in the alpha1-null mice. Tumors implanted into alpha1-null mice showed markedly decreased vascularization, with a reduction in capillary number and size, which was accompanied by an increase in plasma levels of angiostatin due to the action of MMP7 and MMP9 on circulating plasminogen. In vitro analysis of alpha1-null endothelial cells revealed a marked reduction of their proliferation on both integrin alpha1-dependent (collagenous) and independent (noncollagenous) substrata. This reduction was prevented by culturing alpha1-null cells with plasma derived from plasminogen-null animals, thus omitting the source from which to generate angiostatin. Plasma from tumor-bearing alpha1-null animals uniquely inhibited endothelial cell growth, and this inhibition was relieved by the coaddition of either MMP inhibitors, or antibody to angiostatin. Integrin alpha1-deficient mice thus provide a genetically characterized model for enhanced angiostatin production and serve to reveal an unwanted potential side effect of MMP inhibition, increased tumor angiogenesis.

Tissue inhibitor of matrix metalloproteinases-1 impairs arterial neointima formation after vascular injury in mice

The hypothesis that tissue inhibitor of metalloproteinases-1 (TIMP-1) plays a role in neointima formation was tested with the use of a vascular injury model in wild-type (TIMP-1(+/+)) and TIMP-1-deficient (TIMP-1(-/-)) mice. The neointimal area at 1 to 3 weeks after electric injury of the femoral artery was significantly higher in TIMP-1(-/-) as compared with TIMP-1(+/+) mice (0.012+/-0. 0015 versus 0.0033+/-0.0008 mm(2) at 1 week, P<0.005). The medial areas were comparable, resulting in intima/media ratios that were significantly larger in TIMP-1(-/-) as compared with TIMP-1(+/+) arteries (1.2+/-0.22 versus 0.39+/-0.08 at 1 week, P<0.005). Nuclear cell counts in cross-sectional areas of the intima of the injured region were higher in TIMP-1(-/-) as compared with TIMP-1(+/+) arteries (138+/-15 versus 69+/-8 at 1 week, P<0.005). Immunocytochemical analysis revealed that alpha-actin-positive smooth muscle cells (SMCs) at 2 weeks after injury were more abundant in the intima of TIMP-1(-/-) arteries than in that of TIMP-1(+/+) arteries, whereas after 3 weeks the intimal cell population consisted mainly of SMCs in both genotypes. In in vitro scrape-wounding assays, SMCs of TIMP-1(-/-) mice migrated faster than those of TIMP-1(+/+) mice. Zymography of arterial extracts revealed a higher active matrix metalloproteinase (MMP)-2 level at 1 to 3 weeks after injury in TIMP-1(-/-) arteries, whereas active MMP-9 was only detected in TIMP-1(-/-) arteries at 1 week after injury. These data are compatible with a role of TIMP-1 in the impairment of SMC migration and neointima formation after vascular injury, as a result of inhibition of MMP activity.

The pathogenesis of choroidal neovascularization in patients with age-related macular degeneration

Laser photocoagulation and several experimental treatments for choroidal neovascularization (CNV) in patients with age-related macular degeneration attempt to ablate the neovascularization, but do not address underlying angiogenic stimuli. As a result, recurrences are a major problem. Drug treatment to counter the growth of CNV would be a major advance, but its development is impeded by lack of knowledge concerning the stimuli and other molecular signals involved in the pathogenesis of CNV. Herein we explore clues that can be gleaned from clinical, epidemiological, pathological, and experimental data. These suggest that abnormalities of the extracellular matrix of retinal pigmented epithelial (RPE) cells may promote a pro-angiogenic RPE phenotype that contributes to the development of CNV. This provides a general hypothesis that can be tested, but it is also necessary to test hypotheses regarding the specific alterations in gene expression that contribute to CNV. Identification of alterations in gene expression will provide targets for rational design of drug treatment.

Endothelial dysfunction following thrombolysis in vitro

OBJECTIVES

Thrombolytic therapy is frequently used to manage vascular graft thrombosis. However, long-term patency after thrombolysis remains poor. The purpose of this study was to characterise the morphological and functional response of endothelial cells (EC) exposed to a thrombus and subsequently lytic therapy.

METHODS

Human EC were exposed to human whole blood thrombus for 2, 6, 12, and 24 h. The thrombus was lysed with urokinase. Cell morphology was studied with electron microscopy. Northern blot analyses were performed with human c-DNA probes for endothelin-1, thrombomodulin, tissue factor, tissue plasminogen activator, plasminogen activator inhibitor, and triose phosphate isomerase.

RESULTS

EC retraction occurred for each period of incubation. Thrombomodulin expression was increased 2.2-fold at 6 h and 2.4-fold at 24 h. t-PA expression was depressed proportionally to the duration of thrombus exposure. PAI and TF expression transiently increased 1.5-fold at 2 h of exposure and returned to baseline at 6 h. Endothelin expression remained unchanged.

CONCLUSIONS

Except for a transient increase in TF expression and reversal of the tPA/PAI ratio, EC exposed to thrombus do not appear to become actively procoagulant. The increase in TM expression may reflect enhanced thromboresistance. However, EC retraction may be responsible for an increase thrombogenicity of saphenous vein graft after thrombosis and Urokinase therapy.

Assessment of the role of tissue inhibitor of metalloproteinase-1 (TIMP-1) during the periovulatory period in female mice lacking a functional TIMP-1 gene

Tissue inhibitor of metalloproteinase (TIMP)-1 is a multifunctional peptide that has been implicated in the ovulatory process. To assess the function of TIMP-1 during the periovulatory period in vivo, mice incapable of expressing the TIMP-1 gene product were utilized. Twenty-three-day-old TIMP-1-deficient (n = 59) and wild-type (n = 61) female mice were injected with 5 IU eCG, followed 48 h later by an ovulation-inducing dose of hCG (5 IU). Animals were killed at the time of hCG injection (0-h hCG), at 12 h (12-h hCG), or at 24 h post-hCG (24-h hCG) administration. Serum was collected for the assessment of estradiol-17beta (0-h hCG groups) or progesterone content (12- and 24-h hCG groups), while ovaries were removed for either histological preparation or Northern analysis of TIMP-1, TIMP-2, and TIMP-3. The number of healthy and atretic follicles was determined in the 0-h hCG groups, as was the number of oocytes released in the 24-h hCG group. TIMP-1-deficient females in the 0-h hCG group showed reduced levels of ovarian TIMP-2 (0.29-fold decrease, p < 0.05) and TIMP-3 (3.0-fold decrease, p < 0.05) expression compared to wild-type counterparts. No significant difference was detected between genotypes in the 0-h hCG group for number of healthy or atretic follicles or for serum estradiol-17beta concentrations. Additionally, no significant differences were detected between genotypes in the 12- and 24-h hCG groups for serum progesterone concentrations, ovarian TIMP-2 and TIMP-3 expression, or number of oocytes released (24-h hCG group). To assess the effect of TIMP-1 on steroidogenesis in vitro, granulosa cells were obtained from 23-day-old, eCG-primed TIMP-1-deficient and wild-type females. Addition of recombinant human TIMP-1 significantly increased conditioned media estradiol-17beta concentrations in cell cultures from both mutant (1.32-fold over controls; p = 0.02; n = 4) and wild-type females (1.16-fold over controls; p = 0.04; n = 3). It is concluded from this study that TIMP-1 may modulate ovarian TIMP-2 and TIMP-3 mRNA expression during folliculogenesis. In addition, TIMP-1 exhibits steroidogenic activity in vitro, but no evidence was found for regulation of steroidogenesis in vivo.

Regulation of the immune response to peptide antigens: differential induction of immediate-type hypersensitivity and T cell proliferation due to changes in either peptide structure or major histocompatibility complex haplotype

The immunodominant CD4 T cell epitope of the bacteriophage lambda cI repressor protein in several inbred mouse strains can be represented by a peptide encompassing amino acids 12-26. Here, we show that this peptide, and a variety of its sequence variants, can induce immediate-type hypersensitivity in mice. 12-26 variants that differ by as little as single amino acid residues deviate greatly in their ability to induce hypersensitivity. Further, differences in major histocompatibility complex class II alleles appear to be as influential as changes in peptide structure in determining whether hypersensitivity is developed. The ability of a given peptide-class II combination to induce hypersensitivity correlates with production of peptide-specific antibody, but not with ability or inability to induce a T cell proliferative response. Administration of anti-interleukin 4 (IL-4) mAb prevents the development of hypersensitivity, and analysis of cytokine production by T cell hybridomas derived from peptide-immunized mice suggests that whether a given peptide-class II combination can induce hypersensitivity depends on its ability to induce IL-4 production. The data demonstrate that changes in the nature of the epitope(s) recognized by the CD4 T cell population can result in qualitative differences in the response elicited in this population, ultimately leading to dramatic quantitative and qualitative variations in the effector phase of the immune response.