Tissue distribution and biochemical properties of an interspecific tumour-associated gamma foetal antigen

Altered expression and distribution of the cytoskeletal-associated p35 protein in NIH 3T3 cells transformed with the Harvey sarcoma virus v-ras oncogene

1. Cytoskeletal events associated with retroviral oncogene (v-ras)-mediated transformation were studied in NIH 3T3 fibroblasts and their v-ras-transfected counterparts (3T3/H-1 cells). 2. Abnormal microfilament networks seen in 3T3/H-1 cells reflected significant decreases (approximately 90%) in two cytoskeletal-associated proteins (tropomyosin-1, p35). Neither actin content nor actin mRNA levels were altered, however, v-ras transfectants. 3. p35 mRNA activity in both NIH 3T3 and 3T3/H-1 cells was similar although differential compartmentalization of p35 to the detergent-resistant cytoskeletal fraction was evident only in normal fibroblasts. 4. Proper cytoskeletal organization may be a factor in the regulation of p35 mRNA translation in situ or influence the stability of p35 independent of translational rate.

Decreased content of the 35 kDa cytoskeletal protein p35 in Friend erythroleukemia cells exposed to dimethyl sulfoxide and retinoic acid is associated with entrance into a quiescent substrate

1. The effect of all-trans-retinoic acid (RA) on cell cycle kinetics, RNA content, and expression of the 35 kDa cytoskeletal protein p35 in exponentially-growing Friend erythroleukemia (FL) cells was compared with the prototypic differentiation-inducer dimethylsulfoxide (DMSO). 2. Two G1 phase populations of RA-treated FL cells were identified: one with an intermediate RNA content (T-cells) similar to G1 cells in near-plateau-phase control cultures and the other with a very low RNA content (Q-cells) similar to DMSO-differentiated cells; although quiescent, RA-treated cells remained undifferentiated as evidenced by the absence of late-stage markers of erythroid maturation. 3. Decreases in the cellular content of p35 occurred in both DMSO- and RA-treated FL cells, correlating with the onset of accumulation of cells into G1, and stabilized by 48 hr after initial exposure to either inducer. 4. Down-regulation in the cellular p35 content, thus, appears to be linked to entrance of FL cells into a quiescent substrate and independent of the subsequent capacity for erythroid differentiation.

Contact-inhibitory factor induces alterations in the distribution and content of specific cytoskeletal elements in an established line of rat hepatic tumor cells

Established 72/22 rat hepatic epithelial tumor cells, which possess intracellular aggregates of intermediate-sized filaments resembling Mallory-body-like inclusions, were used to assess changes in tumor cell growth and morphology associated with exposure to contact-inhibitory factor (CIF). CIF reduced 72/22 proliferative rate, increased mean population doubling time by 42%, lowered culture saturation densities to 34-50% of control values and inhibited formation of dense foci. These proliferative changes were due to an apparent prolongation of the G1 phase of the cell cycle during the period of CIF exposure. CIF concomitantly induced a marked increase (by 70%) in cell spreading and loss of both the usual tight (epithelioid) cell juxtaposition and typical ordered colony structure characteristic of untreated populations. However, CIF exposure failed to achieve complete cytoarchitectural "normalization" in 72/22 cells (i.e., dispersal of the Mallory-body-like aggregate of intermediate filaments and restoration of a more typical hepatocytic phenotype). Most obvious was a reduction in the integrity of the peripheral band of microfilaments (a structure involved in the maintenance of epithelial cell shape) and a decrease in the content of desmoplakin (a protein component of desmosomal plaques). Changes in these major structural elements appear to be critical events in development of the pleomorphic phenotype and reduced substratum adhesiveness observed during treatment. CIF-related fragmentation of peripheral band structures was not reflected in changes in either the total cellular or cytoskeletal-associated actin contents. The morphologic changes observed under conditions of CIF exposure closely paralleled induced decreases in the cellular content of the actin-associated membrane skeleton protein p35. These data collectively suggest that CIF may act to alter the composition of the cortical skeleton in cultured liver tumor cells.