Spontaneous air space enlargement in the lungs of mice lacking tissue inhibitor of metalloproteinases-3 (TIMP-3)

Tissue inhibitors of metalloproteinases regulate ECM degradation by matrix metalloproteinases (MMPs). We have developed a mouse line deficient for tissue inhibitor of metalloproteinases-3 (TIMP-3), the only TIMP known to reside within the ECM. Homozygous Timp-3-null animals develop spontaneous air space enlargement in the lung that is evident at 2 weeks after birth and progresses with age of the animal. As early as 13 months of age animals become moribund. Lung function, measured by carbon monoxide uptake, is impaired in aged null animals. Lungs from aged null animals have reduced abundance of collagen, enhanced degradation of collagen in the peribronchiolar space, and disorganization of collagen fibrils in the alveolar interstitium, but no increase in inflammatory cell infiltration or evidence of fibrosis in comparison with controls. Using in situ zymography, we show that lungs from aged null animals have heightened MMP activity over wild-type and heterozygotic animals. Finally, TIMP-3-null fibroblast cultures demonstrate enhanced destruction of ECM molecules in vitro. We propose that the deletion of TIMP-3 results in a shift of the TIMP/MMP balance in the lung to favor ECM degradation, culminating in incapacitating illness and a shorter life span.

Accelerated apoptosis in the Timp-3-deficient mammary gland

The proapoptotic proteinase inhibitor TIMP-3 is the only molecule of this family thought to influence cell death. We examined epithelial apoptosis in TIMP-3-deficient mice during mammary gland involution. Lactation was not affected by the absence of TIMP-3, but glandular function, as measured by gland-to-body weight ratio and production of beta-casein, was suppressed earlier during post-lactational involution than in controls. Histological examination revealed accelerated lumen collapse, alveolar-epithelial loss, and adipose reconstitution in Timp-3(-/-) females. Epithelial apoptosis peaked on the first day of involution in Timp-3-null glands but at day 3 in wild-type littermates. Unscheduled activation of gelatinase-A was evident by zymography and correlated with earlier fragmentation of fibronectin in Timp-3(-/-) mammary. To obtain independent evidence of the proapoptotic effects of TIMP-3 deficiency, we introduced recombinant TIMP-3-releasing pellets into regressing Timp-3(-/-) mammary tissue and showed that this treatment rescued lumen collapse and epithelial apoptosis. Ex vivo, involuting Timp-3(-/-) mammary tissue demonstrated accelerated epithelial apoptosis that could be reduced by metalloproteinase inhibition. The physiological relevance of TIMP-3 became apparent as Timp-3(-/-) dams failed to reestablish lactation after brief cessation of suckling. Thus, TIMP-3 is a critical epithelial survival factor during mammary gland involution.

Matrix metalloproteinase-9 maps to the distal end of chromosome 2 in the mouse

The activity and expression of matrix metalloproteinase-9/gelatinase B (MMP-9), an enzyme implicated in the implantation process in mice, was investigated in normal and parthenogenetic blastocyst outgrowths. Conditioned media from parthenogenetic blastocysts after 4 days of culture had reduced levels of MMP-9 activity compared to conditioned medium from normal outgrowths. Levels of MMP-9 mRNA assayed by reverse transcription-polymerase chain reaction methods were also reduced in parthenogenetic blastocysts compared to normal outgrowths. Genetic mapping studies showed that Mmp9 maps to the distal end of chromosome 2 near the proximal boundary of a region affected by genomic imprinting. Both parental alleles of Mmp9, however, are expressed in 11.5-day embryos derived from interspecific crosses of Mus musculus and Mus spretus. Thus, loss of MMP-9 activity in parthenogenetic blastocysts does not appear to be due to imprinting but, rather, due to a defect of trophoblast giant cell proliferation and differentiation.

Cellular turnover and extracellular matrix remodeling in female reproductive tissues: functions of metalloproteinases and their inhibitors

Female reproductive tissues possess a unique ability to accommodate a remarkable amount of cell turnover and extracellular matrix (ECM) remodeling following puberty. Cellular structures within ovary, uterus, and mammary tissue not only change cyclically in response to ovarian hormones but also undergo differentiation during pregnancy, and eventually revert to that resembling the pre-pregnant stage. Cell proliferation, apoptosis, invasion, and differentiation are integral cellular processes that are precisely regulated in reproductive tissues, but become dysregulated in pathologies such as cancer. Explicit reorganization of ECM and basement membranes is also critical to preserve the form and function of these tissues. Here we review the evidence that coordinated spatiotemporal expression patterns of matrix metalloproteinase (MMP) genes and their tissue inhibitors (TIMPs) are important in cell and ECM turnover of the ovary, uterus, and mammary tissues. We discuss how perturbation in these gene families may impact the biology of these reproductive tissues and the factors implicated in the control of MMP and TIMP gene expression. The observed trends in MMP and TIMP expression involved in ovarian and mammary carcinomas are also presented.

Timp-1 is important for epithelial proliferation and branching morphogenesis during mouse mammary development

The dynamic process of mammary ductal morphogenesis depends on regulated epithelial proliferation and extracellular matrix (ECM) turnover. Epithelial cell-matrix contact closely dictates epithelial proliferation, differentiation, and survival. Despite the fact that tissue inhibitors of metalloproteinases (Timps) regulate ECM turnover, their function in mammary morphogenesis is unknown. We have delineated the spatiotemporal expression of all Timps (Timp-1 to Timp-4) during discrete phases of murine mammary development. Timp mRNAs were abundant in mammary tissue, each displaying differential expression patterns with predominant localization in luminal epithelial cells. Timp-1 mRNA was unique in that its expression was limited to the stage at which epithelial proliferation was high. To assess whether Timp-1 promotes or inhibits epithelial cell proliferation we manipulated mammary Timp-1 levels, genetically and biochemically. Down-regulation of epithelial-derived Timp-1 in transgenic mice, by mouse mammary tumor virus promoter-directed Timp-1 antisense RNA expression, led to augmented ductal expansion and increased number of ducts (P < 0.004). In these transgenics the integrity of basement membrane surrounding epithelial ducts, as visualized by laminin-specific immunostaining, was breached. In contrast to these mice, ductal expansion was markedly attenuated in the proximity of implanted recombinant Timp-1-releasing pellets (rTIMP-1), without an increase in basement membrane deposition around migrating terminal end buds. Epithelial proliferation and apoptosis were measured to determine the basis of altered ductal expansion. Luminal epithelial proliferation was increased by 55% (P < 0.02) in Timp-1-reduced transgenic mammary tissue and, conversely, decreased by 38% (P < 0.02) in terminal end buds by implanted rTIMP-1. Epithelial apoptosis was minimal and remained unaffected by Timp-1 manipulations. We conclude that Timps have an integral function in mammary morphogenesis and that Timp-1 regulates mammary epithelial proliferation in vivo, at least in part by maintaining basement membrane integrity.

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis. © 1999 Cancer Research Campaign

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis.

Murine tissue inhibitor of metalloproteinases-4 (Timp-4): cDNA isolation and expression in adult mouse tissues

We have isolated cDNA clones corresponding to a new member of the murine tissue inhibitor of metalloproteinase (TIMP) family, designated Timp-4. The nucleotide sequence predicts a protein of 22,609 Da that contains the characteristic 12 cysteine TIMP signature. TIMP-4 is more closely related to TIMP-2 and TIMP-3 than to TIMP-1 (48%, 45% and 38% identity, respectively). Analysis of Timp-4 mRNA expression in adult mouse tissues indicated a 1.2 kb transcript in brain, heart, ovary and skeletal muscle. This pattern of expression distinguishes Timp-4 from other Timps, suggesting that the TIMP-4 protein may be an important tissue-specific regulator of extracellular matrix remodelling.

Tissue inhibitor of metalloproteinases-3 is the major metalloproteinase inhibitor in the decidualizing murine uterus

Embryo implantation in the mouse is a highly orchestrated process, a key aspect of which is the invasion of trophoblast cells of the blastocyst into the maternal uterine endometrium. Invasion is facilitated via proteinases expressed by trophoblast cells and balanced by expression of inhibitors of proteinases in the maternal decidua. The predominant proteinase expressed by trophectodermal derivatives of the implanting mouse embryo is matrix metalloproteinase-9 (MMP-9; gelatinase B). Using in situ hybridization, transcripts for MMP-9 were detected in trophoblast cells of the embryo from the earliest stage of decidual formation (day 6.0) examined. MMP-9 transcripts were localized to trophoblast giant cells at the periphery of the embryo at the egg cylinder stage (day 7.0). By the neural-fold stage (day 8.5), expression was restricted to giant cells adjacent to the maternal side of the developing placenta, and by day 9.5 few MMP-9-positive cells remained. The major tissue inhibitor of metalloproteinases (TIMP) produced during this period was TIMP-3. Transcripts encoding TIMP-3 were detected from day 6.0-7.0 in the maternal decidua immediately adjacent to embryonic cells expressing MMP-9. The intensity of TIMP-3 expression in later-stage embryos declined in parallel with MMP-9 expression. Maternal TIMP-3 expression also occurred in the absence of embryonic MMP-9 expression in decidual reactions induced by parthenogenetic embryos (where MMP-9 positive cells were not detected) or in oil-induced deciduomas. These results support the hypothesis that MMP-9 is an important mediator of cellular invasiveness during embryo implantation, and that TIMP-3 serves as a regulator within the uterus to restrict invasion to the site of implantation.

The roles of tissue inhibitors of metalloproteinases in tissue remodelling and cell growth

Tissue inhibitors of metalloproteinases (TIMPs) are secreted proteins that block the activities of the extracellular matrix (ECM)-degrading metalloproteinases (MMPs). As key determinants of ECM integrity and turnover, TIMPs are involved in the establishment and maintenance of tissue architecture and may indirectly influence ECM-dependent cells signaling. In addition, TIMPs exert both positive and negative effects on cell growth through mechanisms that are independent of MMP inhibition. The three members of the mammalian TIMP family differ in structure, biochemical properties and expression, suggesting that they have distinct physiological roles. Here, we review recent advances in our understanding of TIMP protein function and gene regulation. We discuss the potential relevance of MMPs and TIMPs in obesity with regard to effects on the processing of tumor necrosis factor-alpha.

Differential effects of transforming growth factor-beta 1 on the expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in young and old human fibroblasts

The balance between the activities of matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) is an important control point in tissue remodeling. Previous studies have demonstrated elevated expression of the MMPs collagenase and stromelysin-1 by aged human diploid fibroblasts compared to early-passage cultures. We show here that aging cells display an altered response to transforming growth factor-beta 1 (TGF beta 1) that selectively affects MMP mRNA expression. In both young and old cells, phorbol myristoyl-13 acetate (PMA) induced the expression of transcripts of collagenase, stromelysin-1, gelatinase-B, TIMP-1, and TIMP-3. In young cells, TGF beta 1 reciprocally modulated PMA-induced MMP and TIMP gene expression leading to reduced levels of transcripts for the MMPs and augmented accumulation of TIMP-1 and TIMP-3 mRNAs. However, repressing effects of TGF beta 1 on collagenase, stromelysin-1, and gelatinase-B RNA expression were not apparent in old cells, though induction of the TIMP genes was unimpaired. By electrophoretic mobility shift analysis the nuclear transcription factors AP1 and serum response factor (SRF) showed reduced levels of DNA binding activities in old fibroblasts compared to young cells. A probe for the TGF beta-inhibitory element (TIE) gave equivalent levels of complexes with nuclear extracts from both types of cells, though of different mobilities. We conclude that the effects of TGF beta 1 on MMP and TIMP gene expression involve different cellular intermediaries, and suggest that altered composition or modification of TIE binding factors in aging cells may underlie the failure of TGF beta 1-mediated transcription repression. This mechanism may contribute to elevated constitutive expression of MMPs in old cells and to the connective tissue deterioration that accompanies the aging process.

Expression and activity of ovarian tissue inhibitors of metalloproteinases during pseudopregnancy in the rat

The present study examined the role of tissue inhibitors of metalloproteinases (TIMPs) in tissue remodeling that occurs during luteal development and regression throughout pseudopregnancy in the rat. Pseudopregnancy was induced in immature female rats by eCG/hCG priming. Animals (n = 4 per time point) were killed on Days 1, 2, 4, 8, 12, 14, and 16 of pseudopregnancy (post hCG administration), and ovaries were removed and analyzed for metalloproteinase inhibitor activity or TIMP-1, TIMP-2, and TIMP-3 mRNA expression. Inhibitory activity was highest in Day-1 samples (41.35 +/- 6.50 inhibitory units), and inhibitor activity significantly decreased (p < 0.05) thereafter to minimal values at Day 12 (8.14 +/- 2.71 inhibitory units). Methylamine hydrochloride treatment, which inactivates macroglobulin-type inhibitors, revealed that the majority of the inhibitor activity in the Day-1 samples (82.6%) and the Day-16 samples (77.3%) could be attributed to TIMPs. To further distinguish the contribution of each TIMP to this activity, Northern analysis for TIMP-1, -2, and -3 was performed. Analysis of TIMP mRNA expression revealed that TIMP-1 transcript expression was highest (p = 0.00009) at Day 1, decreased approximately 3- to 20-fold from Days 2 to 12, respectively, and again increased at Days 14-16. However, TIMP-2 expression did not change (p > 0.05) over any of the time points studied. In contrast to TIMP-1 and TIMP-2 expression, TIMP-3 mRNA expression was lowest during Days 1 and 2 of pseudopregnancy, increased approximately 4-fold at Day 4, peaked at Day 8, and remained elevated throughout the remainder of pseudopregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteinase expression in early mouse embryos is regulated by leukaemia inhibitory factor and epidermal growth factor

Several proteinases from different multigene families have been implicated in the uterine invasion required for establishment of pregnancy in some mammals. In this study, the expression of matrix metalloproteinase gelatinase B (MMP-9), urokinase-type plasminogen activator (uPA) and their inhibitors was investigated during early mouse embryo development. Transcripts for tissue inhibitors of metalloproteinases (TIMP-1,-2,-3) and uPA receptor were detected throughout pre- and peri-implantation development whilst MMP-9 and uPA mRNAs were first detected in peri-implantation blastocysts associated with the invasive phase of implantation. Through use of in situ hybridization, it was shown that MMP-9 transcripts were strongly expressed in the network of trophoblast giant cells at the periphery of implanting 7.5 day embryos and TIMP-3 transcripts were strongly expressed in the decidua immediately adjacent to the implanting embryo. uPA transcripts were preferentially expressed in the ectoplacental cone and its derivatives. Because these proteinases are regulated by growth factors and cytokines in other tissues, the effect of leukaemia inhibitory factor (LIF) and epidermal growth factor (EGF) on their activity was investigated. Both LIF and EGF, like the proteinases, have been implicated in peri-implantation development. Blastocysts collected on day 4 of pregnancy were cultured 2 days in TCM 199 + 10% fetal bovine serum to allow outgrowth followed by 24 hour culture in defined media containing either LIF or EGF. Conditioned media were assayed for uPA activity by a chromogenic assay and MMP activity by gelatin zymography. Both LIF and EGF stimulated uPA and MMP-9 activity in blastocyst outgrowths after 3 days of culture (day 7). Proteinase activity was assayed again at the 5th to 6th day of culture (day 9 to 10). EGF was found to have no effect whereas LIF decreased production of both proteinases. These results demonstrate that proteinase activity in early embryos can be regulated by growth factors and cytokines during the implantation process and, in particular, they demonstrate the possible involvement of LIF in establishment of the correct temporal programme of proteinase expression.

Roles of growth factors during peri-implantation development

Several growth factor ligand and receptor gene products have been shown to play roles during preimplantation mammalian development. Genes for insulin-like growth factors (IGFs), transforming growth factors (TGFs), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) and receptors for insulin, IGF, PDGF, TGF alpha and epidermal growth factor (EGF) are expressed by early embryos of several species including mouse, rat, cow and sheep. Roles of growth factors during early development have been demonstrated by addition of purified growth factors to culture medium or by molecular genetic techniques that interfere with gene expression. In this way, it has been shown that successful development of the blastocyst is dependent on the action of epidermal growth factor (EGF) and leukaemia inhibitory factor (LIF). Recent experiments show that both LIF and EGF stimulate secretion of urokinase-type plasminogen activator (uPA) and gelatinase B/matrix metalloproteinase-9 (MMP-9) in day 7 mouse blastocyst outgrowths. At the same time, tissue inhibitors of MMPs (TIMPs) are also expressed by embryonic, decidual and uterine tissues during the implantation process. It appears that LIF may act directly or indirectly, by inducing the expression of other cytokines, to regulate the temporal and spatial production and activity of proteases and protease inhibitors to create a favourable environment for implantation.

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is an extracellular matrix-associated protein with a distinctive pattern of expression in mouse cells and tissues

We have isolated cDNA clones corresponding to a novel mouse metalloproteinase inhibitor. Five overlapping cDNA clones contain most of the information for a prominent 4.5-kilobase transcript that was detected in RNA from mouse fibroblasts and adult tissues. Sequence analysis revealed an open reading frame (ORF) for a protein of 212 amino acids that is 80% identical to chicken inhibitor of metalloproteinases-3 (ChIMP-3). The 3'-untranslated sequence also showed remarkable conservation with the chicken gene. The ORF directed the expression of a 24-kDa protein in COS-1 cells that localized to the extracellular matrix (ECM). On the basis of these similarities we propose to identify the new gene as murine tissue inhibitor of metalloproteinases-3 (TIMP-3). Mouse C3H 10T1/2 fibroblasts produced a 24-kDa metalloproteinase inhibitor that also localized to the ECM and was recognized by a polyclonal antibody to ChIMP-3. Like TIMP-1, TIMP-3 was highly inducible in mouse C3H 10T1/2 fibroblasts by phorbol ester (PMA), epidermal growth factor (EGF), and transforming growth factor-beta 1, but nuclear run-on assays showed that the on/off transcription kinetics were faster for TIMP-3 than TIMP-1. A major difference in vitro was the stimulation of expression of TIMP-3 by dexamethasone which inhibits EGF- and PMA-induced TIMP-1 transcription. Also, TIMP-3 showed a distinctive pattern of expression in adult tissues with abundant transcripts detected in kidney, lung, and brain but only low levels detected in bone, a prominent location of TIMP-1 transcripts. We propose that TIMP-3 functions in a tissue-specific fashion as part of an acute response to remodeling stimuli.

Characterization of two cis-acting DNA elements involved in the androgen regulation of the probasin gene

The location and sequence of androgen responsive elements (AREs) in the 5'-flanking DNA of the androgen-regulated rat probasin (PB) gene were determined. The DNA- and steroid-binding domains of the rat androgen receptor [glutathione-S-transferase (GST)-AR1] and the DNA-binding domain and hinge region alone (GST-AR2) were expressed in Escherichia coli as isopropyl-B-D-thioglactopyranoside-induced fusion proteins with GST and purified using glutathione affinity chromatography. Band shift assays indicated that the AR1 peptide was at least five times more effective than AR2 in binding to PB 5'-flanking DNA (-426 to +28), although both gave qualitatively similar patterns and were displaced by anti-AR antibodies. DNase I footprinting experiments revealed two putative AREs: one between positions -236 and -223 (ARE-1) and the other between -140 and -117 (ARE-2). Hormonal regulation of PB was determined by cotransfecting reporter constructions containing the PB 5'-flanking region (-426 to +28) linked to the bacterial chloramphenicol acetyl transferase (CAT) gene with androgen, glucocorticoid, or progesterone receptor expression vectors into human prostatic carcinoma cells (PC-3). PB-CAT gene expression was more effectively induced by androgens than by glucocorticoids or progestins. Both 5'- and 3'-deletion mapping of the PB 5'-flanking DNA revealed that ARE-1 and ARE-2 were required for androgen regulation. A single base mutation in either ARE resulted in a more than 95% loss of androgen induction of CAT. In comparable transfection experiments, the PB hormone-responsive elements showed a greater induction by androgens than did mouse mammary tumor virus or tyrosine aminotransferase elements. Thus, the preferential androgen regulation of the PB gene involves the participation of two different cis-acting DNA elements that bind AR.

Expression of metalloproteinases and their inhibitors in primary pulmonary carcinomas

Nine primary pulmonary carcinomas, one metastatic carcinoma, and two malignant pleural mesotheliomas have been analysed for the expression at the mRNA level of metalloproteinases (MPs) and tissue inhibitors of MPs (TIMPs). In situ hybridisation showed TIMP-1 and TIMP-2 transcripts predominantly over tumour stroma and gelatinases evenly distributed over both stromal and tumour cells. While both TIMP-1 and TIMP-2 were expressed in non-neoplastic lungs (NNL) as well as in carcinomas, stromelysin 3 (ST3), 92 kDa gelatinase and interstitial collagenase were expressed only by carcinomas. Expression of these MPs by carcinomas was independent of histologic type and such tumour features as fibrosis or necrosis. The consistent expression of ST3 by all of the carcinomas examined and absence of its expression in NNL indicates that ST3 production is likely associated with the malignant phenotype. However, since 92 kDa gelatinase and interstitial collagenase transcripts were found in some but not all tumour samples, their expression is not a uniform feature of pulmonary carcinomas. The possible prognostic significance of the expression of the latter two enzymes by carcinomas remains to be established.

Differential regulation of TIMP-1 and TIMP-2 mRNA expression in normal and Ha-ras-transformed murine fibroblasts

A cDNA containing the complete coding region of the murine tissue inhibitor of metalloproteinases-2 (TIMP-2) was isolated using reverse transcription-polymerase chain reaction amplification. The predicted murine TIMP-2 amino acid sequence shows 96% identity with human TIMP-2, but only 42% identity with murine TIMP-1. This high degree of evolutionary conservation between the human and mouse proteins suggests that TIMP-2 performs an essential biological function. The expression of the TIMP-1 and TIMP-2 mRNAs was examined in normal and ras-transformed murine fibroblasts. While TIMP-1 transcription was highly serum-inducible in normal murine C3H10T1/2 fibroblasts, TIMP-2 mRNA expression was largely constitutive. A series of ras-transformed derivatives of C3H10T1/2 fibroblasts showed great variability in TIMP-1 expression: some lines retained serum inducibility, others displayed constitutive expression at either high or low levels. In contrast, TIMP-2 expression was insensitive to transformation. Neither TIMP-1 nor TIMP-2 expression at the RNA level, or total TIMP activity in conditioned media could be correlated with the metastatic potential of the ras-transformed lines. Our data demonstrate that the mechanisms that regulate murine TIMP-1 and TIMP-2 expression are distinct arguing for different physiological roles for the two TIMPs.