Protein kinase C (PK-C) and casein kinase II (CK-II) activities were studied in two human colon carcinoma cell lines (HT-29 and CaCO-2) undergoing differentiation in vitro resulting, in small-intestine-like cells. CaCo-2 cells, when grown under standard conditions, appear to undergo spontaneous differentiation. In these cells PK-C and CK-II activities were determined on day 5, 10 and 15. No significant differences in activities were seen either in PK-C or CK-II activity. HT-29 cells, when grown in glucose-free medium can be stimulated to undergo differentiation which is completed within 20 days. PK-C and CK-II activities were determined after 5, 10, 15, 20 and 25 days, respectively. PK-C activity rose from 7.9±3.5 pmole32P/mg protein/min at day 5 to 37.5±14.8 pmole32P/mg protein/min at day 20. After 25 days the activity was reduced to 20.0±7.8 pmole32P/mg protein/min. CK-II activity did not change significantly during day 5 to 20, but on day 25 there was a significant decrease in CK-II activity from 94.9±6.4 pmole32P/mg protein/min (day 20) to 62.6±3.9 pmole32P/mg protein/min (day 25) p=0.003. The results in this study indicate a role for PK-C and CK-II in cell growth and differentiation.

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