Collagen expression in embryonic chicken chondrocytes treated with phorbol myristate acetate.

Abstract

Growth of embryonic chicken sternal chondrocytes in the presence of phorbol-12-myristate-13-acetate (PMA), a potent tumor promoter, resulted in a dramatic morphological change from spherical floating cells to adherent fibroblastic cells. This morphological change was accompanied by a quantitative switch from synthesis of cartilage-specific type II procollagen to type I procollagen. Type II procollagen mRNA levels decreased 10-fold in PMA-treated cells. Activation of type I collagen genes led to the accumulation of type I procollagen mRNA levels comparable to those of type H mRNA in these cells. However, only type I procollagen mRNA was translated. In addition to gene activation, unprocessed pro al(l) transcripts present at low levels in control chondrocytes were processed to mature mRNA species. Redifferentiation of PMA-treated chondrocytes was possible if cells were removed from PMA after the morphological change and cessation of type H procollagen synthesis but before detectable amounts of type I procollagen were synthesized. Production of type I collagen thus marks a late phase of chondrocyte "dedifferentiation" from which reversion is no longer possible. Redifferentiated cell populations contained 24-fold more pro al(II) collagen mRNA than pro al(I) collagen mRNA, but the rates of procollagen synthesis were comparable. This suggests that the PMA-mediated dedifferentiation of chondrocytes as well as their redifferentiation is under both transcriptional and posttranscriptional regulation.In vivo and in vitro, differentiated chondrocytes secrete and are imbedded in an extracellular matrix composed of type II collagen (16,36,44,50), several minor collagens specific to hyaline cartilage (33), and chondrocyte-specific type IV sulfated proteoglycans (14,20). The latter can be identified because they stain with toluidine blue (13). Chondrocytes in culture are either spherical and remain in suspension or attach to the culture dish and assume a characteristic polygonal morphology (50). When subcultured in monolayer, the cells gradually assume a more fibroblast-like morphology. Morphological changes are followed by a decrease in the expression of the chondrocyte matrix components, including type II collagen and type IV sulfated proteoglycans. Concomitantly, low levels of type I collagen and fibronectin, characteristic of the extracellular matrix of fibroblasts in skin, bone, and tendons are produced. These changes are not the result of overgrowth by contaminating fibroblasts since the switch from type II to type I collagen production can be observed in the progeny of a cloned chondrocyte (10,15,34). The failure to continue to produce the differentiated phenotype led to the characterization of this switch as "dedifferentiation" (22). This is not meant to imply that the cells had returned to an uncommitted or multipotent state, but rather that adverse environmental conditions have interrupted the expression of the differentiated phenotype, somewhat like the heat shock effect. As a result, the cells either revert to an ea...

ERK-1/2 and p38 Kinase Oppositely Regulate Nitric Oxide-induced Apoptosis of Chondrocytes in Association with p53, Caspase-3, and Differentiation Status

“…In addition to NO effects, the differentiated phenotype of chondrocytes is rapidly lost through other environmental changes such as exposure to phorbol ester (44) or during a serial monolayer culture (43). Signaling pathways during chondrocyte dedifferentiation are not clearly understood.…”

“…We therefore further investigated the relationship between NO-induced dedifferentiation and apoptosis in chondrocytes. For this purpose, chondrocytes were passaged to P4 by a serial monolayer culture or treated with 100 nM phorbol 12-myristate 13-acetate (PMA) for 2 days to cause dedifferentiation (43,44). Under these conditions, expression of type II collagen and synthesis of proteoglycan was almost completely inhibited (Fig.…”

Altered beta-actin gene expression in phorbol myristate acetate-treated chondrocytes and fibroblasts.

“…A compilation of the data obtained from the chondrocytes for actin and fibronectin is presented in Fig. 6, and it was compared to the data obtained for type I and type II collagen (14). Such a comparison revealed several interesting correlations.…”

Phorbol ester-mediated downregulation of tropoelastin expression is controlled by a posttranscriptional mechanism

“…For example, TPA mediates differentiation of U937 cells, a human premonocytic cell line, to a phenotype resembling that of circulating monocytes or tissue macrophages (Mitchell et al, 1985), and in chick chondrocytes, TPA exposure leads to apparent dedifferentiation as indicated by a switch from expression of type I1 to type I collagen (Finer et al, 1985). In addition, TPA mediates the regulation of cell-specific protein expression by transcriptional or posttranscriptional mechanisms (Sherman et al, 1990;Zhu et al, 1991).…”