Control of types I and II collagen and fibronectin gene expression in chondrocytes delineated by viral transformation.

Abstract

We have analyzed the effects of transformation by Rous sarcoma virus on expression of types I and II collagen and fibronectin genes in vertebral chondrocytes and compared them with expression of these genes in skin fibroblasts. Transformed chondrocytes display a dramatically decreased amount of type II collagen RNA, which can account fully for the decreased synthetic rate of this protein. Paradoxically, these cells also display greatly increased amounts of type I collagen RNAs, which are translated efficientlv in vitro, but not in the intact cells. We show here that the type I collagen RNAs in transformed chondrocytes are nearly indistinguishable from those found in skin fibroblasts, and that they clearly differ from the type I collagen RNAs found in normal chondrocytes. Transformed chondrocytes also display an increased amount of fibronectin RNA, which can account fully for the increased synthetic rate of this protein. Thus, the effects of transformation by Rous sarcoma virus on type I collagen and fibronectin RNAs in chondrocytes are the opposite of those observed in fibroblasts, which display decreased amounts of these three RNAs. These data indicate that the effects of transformation on the genes encoding type I collagen and fibronectin must be modulated by host cell-specific factors. They also imply that the types I and II collagen genes may be regulated by different mechanisms, the type I genes being controlled at both transcriptional and posttranscriptional levels, and the type II gene being controlled primarily at the transcriptional level.Transformation of differentiated cells by tumor viruses has provided a useful tool for analyzing the mechanisms of cellular gene expression. This has been particularly true for the genes encoding extracellular matrix proteins, whose expression is decreased by transformation with certain viruses. For example, transformation of chicken embryo fibroblasts by Rous sarcoma virus (RSV) results in reduced synthesis of type I collagen (10,20,25,(45)(46)(47) and, in some cases, fibronectin (36,39). Similarly, transformation of chicken vertebral chondrocytes by RSV results in decreased synthesis of type II collagen and the major cartilage proteoglycan (2,18,37,38). The reduced rates of synthesis of type I collagen and fibronectin in transformed fibroblasts reflect decreased amounts of the corresponding RNAs (1, 3. 15,19,43,45,46,51) These data demonstrate that transformation by RSV has opposite effects on the expression of type I collagen and fibronectin genes in chondrocytes and fibroblasts and imply that the action of src is modulated by host cell factors that differ between these cell types. They also imply that the types I and II collagen genes may be regulated by different mechanisms. The genes encoding type I collagen, a protein which is synthesized by many cell types, appear to be regulated at both transcriptional and posttranscriptional levels. In contrast, the type II collagen gene, which is expressed only by a very limited number of terminally differentiated cell type...

Collagen gene expression during limb cartilage differentiation.

“…An unexpected finding of considerable interest was the presence of low levels of type II collagen mRNA in the cytoplasm of prechondrogenic mesenchymal cells at the earliest stages of limb development, indicating the type II collagen gene is being transcribed well before the onset of overt cartilage differentiation and the accumulation of detectable amounts of type II collagen. Furthermore, our results are consistent with other recent studies (1,9,31) indicating that type I collagen gene expression during chondrogenesis is regulated, at least in part, at the translational level, since substantial amounts of type I collagen mRNAs are present in the cytoplasm of well-differentiated chondrocytes which do not synthesize detectable amounts of type I collagen.…”

“…Evidence for the translational regulation of type I collagen gene expression in chondrocytes has also recently been provided by other investigators. Type I collagen mRNAs have been detected in limb and sternal cartilage (22); in the cytoplasm of cultured sternal chondrocytes (31); and in cultured vertebral chondrocytes, which also do not synthesize type I collagen (1,9).…”

Inhibition of chicken embryo lens differentiation and lens junction formation in culture by pp60v-src.

“…The transformation also disrupts the expression of the normal differentiation program of the cells. This suppression of the expression of normal cell differentiation parallels the results which have been reported for other cell systems, including retinal melanoblasts (7,26), myoblasts (11,14,22), and chondroblasts (1,3,23). In the myogenic and chondrogenic cells the suppression of differentiation is seen as a suppression of the synthesis of normal differentiation products.…”

“…The major products of chondrogenic differentiation are the components of their extracellular matrix. The synthesis of these components is coordinately suppressed by v-src and appears to be regulated primarily at the mRNA level (1,3). In addition to the suppression of synthesis, the expression of v-src may affect morphological differentiation by other mechanisms.…”

Immortalization of Rat Growth Cartilage Cells by Retro Virus Carrying C-myc Oncogene and Their Histochemical and Immuno-Histochemical Characteristics.

“…Virus carrying oncogenes cause transformation or immortalization of chondrocytes and/or osteocytes [1,8,27,29]. Myc oncogene is known as an immortalizing gene [5,6,9].…”