Regulation of Bcl-2 protein expression in human neuroblastoma SH-SY5Y cells: Positive and negative effects of protein kinases C and A, respectively

The regulatory mechanism of Bcl-2 protein expression was investigated in SH-SY5Y cells, the human neuroblastoma cell line that expresses natively Bcl- 2 proteins. When the cells were treated with 12-O-tetradecanoylphorbol 13- acetate (TPA) or retinoic acid, the level of Bcl-2 protein was increased compared with the control. These effects were inhibited by pretreatment with a protein kinase C (PKC) inhibitor, staurosporine or calphostin C. The level of Bcl-2 protein was also increased by treatment with carbachol, a muscarinic acetylcholine receptor (mAChR) agonist, and the effects were also inhibited by pretreatment with staurosporine or calphostin C. In addition, a carbachol- induced increase in Bcl-2 protein levels and a transient elevation of [Ca²⁺](i) were inhibited by pretreatment with 4-DAMP (4-diphenylacetoxy-N- methylpiperidine), an m₃ mAChR antagonist. In contrast, the level of Bcl-2 protein was decreased by treatment with dibutyryl cAMP (diBu-cAMP), forskolin, or cholera toxin, and the effects of diBu-cAMP were inhibited by pretreatment with a protein kinase A (PKA) inhibitor, H-89. From these results, we suggest that the expression of Bcl-2 proteins is regulated by PKC and PKA in positive and negative manners, respectively, in SH-SY5Y cells. Furthermore, the nucleosomal DNA fragmentation induced by serum depletion for 4 h was observed in SH-SY5Y cells when the level of Bcl-2 protein was down- regulated by treatment with 1 mM diBu-cAMP for 3 days, although the DNA fragmentation by serum depletion for 4 h was not observed in nontreatment cells, indicating that Bcl-2 proteins whose expression is regulated by PKC and PKA play important roles in serum depletion-induced apoptosis.