Calmodulin‐Binding Proteins in Human Y‐79 Retinoblastoma and HTB‐14 Glioma Cell Lines

Abstract: The Y‐79 human retinoblastoma cell line has been used as a model system for studying differentiation of primitive neuroectodermal cells into either glial‐like (glial fibrillary acidic protein positive) or neuron‐like (neuron‐specific enolase‐positive) cells. To determine whether Y‐79 retinoblastoma cells express neuronotypic calmodulin‐binding proteins, Y‐79 cells were either treated with butyrate or dibutyryl cyclic AMP (dbcAMP) in serum‐containing medium or were maintained in serum‐free media. Using a biotinylated calmodulin blot overlay technique, we found that Y‐79 cells treated with dbcAMP or butyrate expressed low levels of membrane‐bound calmodulin‐binding proteins of 150, 147, 127, and 126 kilodaltons (kDa); butyrate‐treated cells also expressed a calmodulin‐binding peptide of 135 kDa. Since butyrate treatment of Y‐79 cells induces the expression and the secretion of interphotoreceptor retinoid‐binding protein (IRBP, 140 kDa), we tested the hypothesis that the calmodulin‐binding protein of 135 kDa induced by butyrate treatment was IRBP. Purified bovine IRBP did not bind calmodulin; further, the 135‐kDa calmodulin binding protein was not immunoreactive with antisera directed against IRBP. Since dbcAMP and butyrate induce some glial‐like characteristics in Y‐79 cells, we compared the calmodulin‐binding protein pattern in these cells with that seen in human HTB‐14 glioma cells. The HTB‐14 line did not express calmodulin‐binding proteins, even after treatments with agents that induce morphologic change in these cells. Thus, we conclude that Y‐79 cells express membrane‐bound calmodulin‐binding proteins, but in a pattern different from that seen with adult, differentiated neurons or from human HTB‐14 glioma cells.