Regulation of the production of a prolactin-like protein (MRP/PLF) in 3T3 cells and in the mouse placenta

Mrp3, a mitogen-regulated protein/proliferin gene expressed in wound healing and in hair follicles

During cutaneous wound healing, a marked increase in the local expression of growth factors results in increased migration and proliferation of the cells responsible for tissue repair. The mitogen-regulated protein (MRP)/proliferin proteins are growth factors and angiogenesis factors. Here it is demonstrated that Mrp3 is induced in wound edge keratinocytes during cutaneous wound healing and also temporally appears in the outer root sheath of the hair follicle during the late anagen phase of the hair cycle. In cultured keratinocytes, Mrp3 is induced by keratinocyte growth factor, but not by epidermal growth factor or by transforming growth factor type alpha. Transgenic mice, expressing lacZ under the combined control of the cytomegalovirus immediate early enhancer and the Mrp3 flanking sequences, demonstrate wound- and hair cycle-induced transgene expression. These results show that elements within the flanking regulatory sequences of the Mrp3 gene are involved in the activation of Mrp3 in response to these events. The results reported here suggest that MRP3 may participate in wound healing and hair follicle cycle as a growth factor and/or angiogenesis factor.

Signaling between the placenta and the uterus involving the mitogen-regulated protein/proliferins

The aim of this investigation was to examine signaling between the placenta and uterus during pregnancy. To do this, we determined the tissue messenger RNA and protein levels of members of a glycopeptide hormone family known to stimulate the proliferation of uterine cells and related these levels to the growth of the uterus during pregnancy in the mouse. This hormone family is known as mitogen-regulated protein (MRP); alternatively proliferin (PLF). Three mrp/plf genes, plf1, mrp3 and mrp4, are expressed by the placenta with different developmental profiles. The major increase of about 4-fold in DNA content of the uterus occurs between days 9 and 14 when MRP/PLFs are present in the placenta. By contrast, the gestational changes in estradiol-17beta levels in placental and uterine tissues and in circulation do not correlate with the period of uterine growth. The previously reported mitogenic activity of the MRP/PLFs and their gestational profiles suggest that one or more of these proteins stimulates uterine proliferation during gestation. Evidence is also presented that expression of MRP3 and/or PLF1, but not MRP4, is negatively regulated by feedback from the uterus. Our results are consistent with the hypothesis that MRP/PLFs stimulate uterine proliferation in vivo and that a uterine factor shuts off PLF1 and/or MRP3 synthesis in the latter half of gestation.

The half-life of human procathepsin S

Two processes, synthesis and degradation, contribute to the intracellular concentration of a protein. As most malignant tumors or tumor cell lines show elevated levels of proteinases, we studied the half-life of a cysteine proteinase, procathepsin S, in order to determine whether tumor cells can regulate their cathepsin concentration via changing the degradation rate of the enzyme. The following procathepsin S species were examined: wild-type procathepsin S in macrophages, recombinant procathepsin S in human embryonic kidney cells (HEK 293 cells), recombinant nonglycosylated procathepsin S in HEK 293 cells, wild-type procathepsin S in the established nonsmall cell lung carcinoma cell line 97TM1. The half-lives of both wild-type procathepsins S expressed in macrophages and in HEK 293 cells were 1 h, whereas that of procathepsin S in the tumor cell line was 2 h. Nonglycosylated procathepsin S was not processed. The degradation of mature cathepsin S proceeded with a half-life of 16-18 h. All cell lines studied secreted substantial amounts of procathepsin S into the culture medium. No further maturation of secreted procathepsin S has been observed in the culture medium. We suggest a disturbed sorting mechanism in tumor cells.

Instability of endogenous MRP/proliferin transcripts in the nucleus of mouse embryo fibroblasts contrasts with their stability when produced during transient transfections

The mitogen regulated protein/proliferin (MRP/PLF) gene is transcribed in primary mouse embryo fibroblasts (MEFs), but the pre-mRNA is not properly converted into a stable cytoplasmic mRNA and instead is rapidly degraded, apparently in the nucleus [Malyankar et al. (1994): Proc Natl Acad Sci USA 91:335-359]. In 3T3 cells derived from the MEFs by the standard 3T3 immortalization protocol, stable MRP/PLF mRNA is produced. We show here that the processing of intron sequences is similar in the two cell types and that some of the MRP/PLF transcripts are polyadenylated in the MEFs. We also document the production of stable MRP/PLF mRNA generated by transcription of various plasmid constructs containing different portions of the MRP/PLF3 gene after calcium phosphate-mediated transfection into the MEFs. We conclude that the inability of the MRP/PLF mRNA to accumulate in the MEFs is unlikely to result solely from a single localized sequence in the primary transcript (or the mRNA) that causes it to be subject to rapid breakdown; possibly export of the mRNA from the MEF nucleus is defective or some aspect of the transcriptional process marks the transcript for degradation.

Developmental expression of cathepsin L and c-rasHa in the mouse placenta

An investigation is described of the expression of the cysteine proteinase cathepsin L during placental development. In addition, whether cathepsin L expression is linked to c-rasHa expression in development, as it is in metastatic cells, is examined. Large amounts of cathepsin L and its transcript are present in the mouse placenta, more than six times more than in adult kidney and liver. Throughout gestation, cathepsin L and its transcript are located in the giant cells and spongiotrophoblasts of the placenta. Several forms of different mobility on denaturing gels are found in the placenta. Their apparent molecular weights, as determined from the gels, are 43,000, 39,000, 29,000, and 20,000. The 39-kDa form is procathepsin L. The 29-kDa and 20-kDa forms are lysosomal cathepsin Ls. The 39-kDa procathepsin L and the 20-kDa mature cathepsin L are the most abundant species in the placenta and are present in about equal amounts throughout gestation. At any time during gestation, placental minces synthesize and secrete only procathepsin L. The amniotic fluid of the fetus contains the 43-kDa form of cathepsin L and procathepsin L, but no detectable amounts of mature cathepsin L. By contrast, serum from nonpregnant or pregnant mice contains three forms of cathepsin L (i.e., the 43-kDa form, procathepsin L, and mature cathepsin L). Cathepsin L and the rasHa oncogene are expressed in two coincident waves corresponding to periods during which the placenta is invasive and just before parturition. The presence of large amounts of cathepsin L in the placenta suggests that the proteinase has a significant function there. Expression of cathepsin L in the placenta is potentially under the control of the ras gene product p21; both are under developmental control.

Regulation of the expression of mitogen-regulated protein (MRP; proliferin) and cathepsin L in cultured cells and in the murine placenta

The genes encoding mitogen-regulated protein (MRP; also called proliferin; PLF) and procathepsin L (CL; also called major excreted protein; MEP) are expressed to high levels in the mouse placenta. Although they are both regulated by epidermal growth factor (EGF) and fibroblast growth factor (FGF) in 3T3 cells, expression of these genes is differently regulated with growth state. The expression patterns of MRP and CL as a function of murine development are also different. Basal and growth factor-stimulated levels of MRP expression are much higher in growing than in quiescent 3T3 cells, whereas CL levels are similar. These changes in gene expression in cultured quiescent cells parallel the changes in MRP and CL expression observed in the late-gestational quiescent placenta. These results suggest growth factors may regulate the expression of these genes, but other influences also regulate the expression of MRP and CL in vivo.

Characterization of a mouse mitogen-regulated protein/proliferin gene and its promoter: a member of the growth hormone/prolactin gene superfamily

A genomic clone containing the complete gene, designated mrp/plf3, of a member of the mitogen-regulated protein/proliferin (MRP/PLF) multi-gene family was isolated from a mouse genomic library constructed in lambda L47.1. The DNA sequences of the 5' flanking region, the exons, and the exon/intron boundaries have been determined. The size and organization of the five exons in the murine mrp/plf3 gene are very similar to those of members of the prolactin/growth hormone family, confirming that mrp/plf3 is a part of this superfamily. Removal of an upstream negative regulatory element revealed an active mrp/plf promoter that was responsive to TGF-alpha and contains known regulatory elements. Intracellular mrp/plf mRNA levels were increased by 17 beta-estradiol and reduced by dexamethasone.

Antipeptide antibodies reveal structural and functional characteristics of rat placental lactogen-II

The purpose of this investigation was to develop specific immunologic probes to rat placental lactogen-II (PL-II) and to use the immunologic probes to further characterize rat PL-II. Five oligopeptides corresponding to different regions of rat PL-II (amino acids 1-13, 56-70, 89-103, 107-118, 150-164) were chemically synthesized by solid phase methods and purified to homogeneity by reverse phase high performance liquid chromatography. The synthetic peptides were coupled to keyhole limpet hemocyanin (KLH) and the peptide-KLH conjugates were used to immunize rabbits. Antibody production was monitored by enzyme-linked immunoassay (EIA), electrophoresis and immunoblotting analyses. Each of the antipeptide antisera showed reactivity with the entire rat PL-II protein; however, the extent of the reactivities of each antiserum with rat PL-II was dependent on the conformational state of rat PL-H. Antisera directed to amino acids 56-70 showed the best reactivity toward each of the conformational states of rat PL-II tested. Antibodies generated to the entire rat PL-II protein specifically recognized the 56-70 amino acid sequence but showed limited reactivity with synthetic peptide corresponding to amino acids 1-13, 89-103, 107-118, and 150-164 of rat PL-II. Antisera to amino acids 56-70 of rat PL-II were specific for PLs as demonstrated by their recognition of rat PL-II, mouse PL-II and human PL and by their lack of reactivity with rat pituitary prolactin and growth hormone and with a series of other synthetic peptides to rat PL-II and rat prolactin-like protein-A. The immunorecognition of human PL was restricted to antipeptide antibodies directed to amino acids 56-70 of rat PL-II. The chemically synthesized peptides representing various regions of rat PL-II did not show significant interactions with prolactin receptors, and antisera directed to the peptides failed to interfere with the binding of either rat PL-II or human PL to prolactin receptors. In summary, we have generated a series of immunologic probes for studying the structure of rat PL-II. The sequence comprising amino acids 56-70 of rat PL-II was shown to make up at least part of an epitope for rat PL-II and to be a region of significant structural homology with mouse PL-II and human PL.