NEURONAL DIFFERENTIATION IS ACCOMPANIED BY NSP-C EXPRESSION

Neuroendocrine-specific protein (NSP) reticulons are expressed in neur al and neuroendocrine tissues and cell cultures derived therefrom, whi le most other cell types lack NSP-reticulons. Three major subtypes hav e been identified so far, designated NSP-A, NSP-B, and NSP-C. We have investigated the correlation between the degree of neuronal differenti ation, determined by morphological and biochemical criteria, and NSP-r eticulon subtype expression. For this purpose, several human neuroblas toma cell lines, exhibiting different degrees of neuronal differentiat ion, were examined immuno(cyto) chemically. It became obvious that the expression of NSP-C, as detected by immunofluorescence microscopy and Western blotting, is most prominent in cell lines with a high degree of neuronal differentiation, such as LA-N-5. Such highly differentiate d cells also express other neural and neuroendocrine markers, such as neural cell adhesion molecule (NCAM), neurofilament proteins, synaptop hysin, and chromogranin. NSP-A was observed in all cell lines to a dif ferent extent. However, no clear correlation was observed with the deg ree of neuronal differentiation as defined by other neuronal and neuro endocrine markers or morphology. NSP-B could not be detected. The indu ction of neuronal differentiation with nerve growth factor, dbcAMP, an d retinoic acid in the rat pheochromocytoma cell line PC12 and the hum an teratocarcinoma cell line hNT2, respectively, induced the expressio n of NSP-A and NSP-C in these cell lines parallel to the induction of neurofilament protein expression. It is concluded that NSP-C expressio n, in particular, is strongly correlated with neuronal differentiation .