Phorbol-ester-mediated expression of the collagen type I pro-alpha 2 gene in mouse 3T3-L1 cells and its absence in a phorbol 12-myristate 13-acetate-non-responsive variant

Factors involved in the regulation of type I collagen gene expression: implication in fibrosis

Type I collagen, the major component of extracellular matrix in skin and other tissues, is a heterotrimer of two alpha1 and one alpha2 collagen polypeptides. The synthesis of both chains is highly regulated by different cytokines at the transcriptional level. Excessive synthesis and deposition of collagen in the dermal region causes thick and hard skin, a clinical manifestation of scleroderma. To better understand the causes of scleroderma or other tissue fibrosis, it is very important to investigate the molecular mechanisms that cause upregulation of the Type I collagen synthesis in these tissues. Several cis-acting regulatory elements and trans-acting protein factors, which are involved in basal as well as cytokine-modulated Type I collagen gene expression, have been identified and characterized. Hypertranscription of Type I collagen in scleroderma skin fibroblasts may be due to abnormal activities of different positive or negative transcription factors in response to different abnormally induced signaling pathways. In this review, I discuss the present day understanding about the involvement of different factors in the regulation of basal as well as cytokine-modulated Type I collagen gene expression and its implication in scleroderma research.

Hyaluronidases and CD44 undergo differential modulation during chondrogenesis

Hyaluronan, a high-molecular-weight glycosaminoglycan of cartilage, is deposited directly into the extracellular space by hyaluronan synthases, while hyaluronan catabolism is mediated by the hyaluronidases. An in vitro cell culture system has been established in which human dermal fibroblasts are induced to undergo chondrogenesis. Here, we describe the differential modulation of the hyaluronidases and the up-regulation of the hyaluronan receptor, CD44, during such chondrogenesis. Dermal fibroblasts, plated in micromass cultures in the presence of lactic acid and staurosporine for 24 h, were then placed in serum-free, chemically defined medium. At 3 days, RNA was extracted and RT-PCR performed using primers for the hyaluronidase genes. Marked increase in HYAL1 expression was observed, with only moderate increases occurring in HYAL2 and HYAL3. No expression of HYAL4 and PH-20, the sperm-associated hyaluronidase, was detected. RNA levels correlated well with changes in hyaluronidase enzyme activity. Finally, greater expression and staining for the hyaluronan receptor, CD44s, the standard form, were detected. Differential expression of the somatic hyaluronidases and CD44-mediated hyaluronan turnover play a critical role in cartilage development from mesenchymal precursors.

Phosphorylation of DNA topoisomerase I is increased during the response of mammalian cells to mitogenic stimuli

DNA topoisomerase I is phosphorylated after mitogenic stimulation of 3T3-L1 mouse fibroblasts by 12-O-tetradecanoylphorbol 13-acetate (TPA), a phorbol ester tumor promoter. In vivo labeling with [32P]orthophosphate and immunoprecipitation with an anti-DNA topoisomerase I antibody has demonstrated an increase in the phosphorylation of DNA topoisomerase I in Swiss/3T3 mouse fibroblasts treated with epidermal growth factor (EGF) and H35 rat hepatoma cells treated with insulin. The only phosphorylated form of DNA topoisomerase I observed was the 100-kDa protein Digestion of DNA topoisomerase I with trypsin revealed two phosphopeptides. In addition, VT-1, a non-responsive genetic variant of 3T3-L1, and the DNA topoisomerase I inhibitor camptothecin were used to further study TPA-induced DNA topoisomerase I phosphorylation. Our results indicate that the phosphorylation of DNA topoisomerase I may be an ubiquitous response of cultured mammalian cells to mitogenic agents, even in the absence of DNA replication.