INTRACELLULAR CA2-BINDING PROTEINS IN CHEMICALLY TRANSFORMED RAT FIBROBLASTS( AND CA2+)

Disturbed Ca2+ handling and altered levels Ca2+-binding proteins (CaBP s) have been found many transformed cells. To investigate whether ther e exists a correlation between expression of CaBPs and intracellular C a2+ we analyzed three transformed rat fibroblast cell lines (T14, T10, and T43) exhibiting different levels of CaBPs. All three cell lines e xpress calmodulin (CaM) at elevated levels compared to normal tissues. In addition, oncomodulin (OM) is expressed at high levels in T14 cell s and at much lower levels in T10 cells, while T43 cells do not expres s OM. We demonstrate that CaBP levels are affected by changes of extra cellular [Ca2+] ([Ca2+]0()). In reduced [Ca2+](0), CaM levels were inc reased up to 60%, while OM levels were decreased up to 65% in T14 and T10 cells. Increase of [Ca2+](0), on the other hand, led to a decrease of CaM levels and an increase of OM levels, suggesting that [Ca2+](0) exerts its effect on OM and CaM differently. Comparison of the growth rates in reduced [Ca2+], revealed that T14 cells with the most pronou nced CaM increase induced by low [Ca2+], grew best under these conditi ons. These results indicate that elevated CaM expression but not the p resence of OM reduces the Ca2+ requirement for growth. Intracellular [ Ca2+] transients are not buffered by the high concentration of CaBPs i n T14 cells. In contrast, [Ca2+](i) transients induced by increase of [Ca2+](0) or addition of serum were most pronounced in T14 cells compa red to T10 and T43 cells. (C) 1994 Academic Press, Inc.