ASCORBATE-INDEPENDENT PROLINE HYDROXYLATION RESULTING FROM VIRAL TRANSFORMATION OF BALB 3T3 CELLS AND UNAFFECTED BY DIBUTYRYL CAMP TREATMENT

Collagen synthesis, hydroxylation of proline in collagen and collagen secretion were studied in the contact-inhibited mouse fibroblast line Balb 3T3, the Kirsten virus transformed line Ki-3T3 and dibutyryl cAMP (dbcAMP)-treated Ki-3T3 cells during the various phases of the growth cycle. Transformed cells in log and stationary phase produced lower levels of collagen than the parent line, but 85-90% of the theoretically possible hydroxyproline residues of the collagen were formed even when ascorbic acid was not added to the culture medium. The transformed cells showed only about a 20% increase of collagen secretion upon addition of ascorbate. This was in contrast to the ascorbate requirement for maximal proline hydroxylation and the 2-3 fold stimulation of collagen secretion by ascorbate in the parent Balb 3T3 cells. Although dbcAMP treatment caused Ki-3T3 cells to assume a more normal morphology and increased the relative rate of collagen synthesis to levels similar to that of 3T3, such treatment did not restore an ascorbate requirement for proline hydroxylation or collagen secretion. The specific activity of the enzyme prolyl hydroxylase also was not affected by dbcAMP treatment, although collagen synthesis was increased by such treatment. Ascorbic acid was not effective in activating prolyl hydroxylase derived from Ki-3T3 or dbcAMP-treated Ki-3T3 cell cultures in log phase or stationary phase. Ki-3T3 cultures did not accumulate ascorbic acid in cells or medium, nor was ascorbic acid synthesized from the precursor 14C-glucuronate in cell homogenates. Virally transformed Balb 3T3 cells apparently acquire the capacity to synthesize a reducing cofactor for prolyl hydroxylase, and this function may be related to the increased glycolytic metabolism of these cells, since neither cellular metabolism nor ascorbate-independent hydroxylation was altered by treatment with dbcAMP.