Effects of dibutyryl cAMP on stanniocalcin and stanniocalcin-related protein mRNA expression in neuroblastoma cells

Stanniocalcin is a polypeptide hormone that was first reported in fish as a regulator of mineral metabolism. Its recent identification in mammals has opened a new area of investigation in basic and clinical endocrinology. In the present study, regulation of the stanniocalcin (STC) and stanniocalcin related protein (STCrP) genes were investigated in mouse neuroblastoma cells (Neuro-2A) in relation to neuronal cell differentiation. Neuro-2A is an undifferentiated cell line that contains measurable levels of STCrP mRNA, but undetectable levels of STC mRNA. Treatment of the cells with either dbcAMP (1-4 mM) or 50 μM euxanthone (PW1) resulted in extensive differentiation and neurite outgrowth. However, only neurites of dbcAMP-treated cells developed varicosities, a phenotypic marker of axon formation. Furthermore, following differentiation induced by dbcAMP, there was an upregulation of STC and downregulation of STCrP mRNA levels. In the first 24 and 48 h of treatments, there was a maximum twofold induction and 1.5-fold reduction in STC and STCrP mRNAs respectively. Following 96 h of treatment, an additional 14-fold STC induction and 1.2-fold STCrP reduction were observed. The increase in STC mRNA levels was accompanied by a concomitant increase in axon-specific low molecular form microtubule-associated protein (MAP-2c) mRNA and varicosities on the neurites, suggesting a possible role for STC in axonogenesis. There was no induction of STC mRNA levels when PW1 was added into the culture media, whereas ionomycin (1-10 μM) had no observable effects on cell differentiation or STC/STCrP mRNA. Immunocytochemical staining of dbcAMP-treated cells revealed abundant levels of immunoreactive STC, particularly in the varicosities, with only weak staining in control, untreated cells. Antisense oligodeoxynucleotides transfection studies indicated that the expression of STC was a cause of varicosity formation and a consequence of cell differentiation. Our findings lend further support to the notion that STC is involved in the process of neural differentiation.