Hippocalcin Promotes Neuronal Differentiation and Inhibits Astrocytic Differentiation in Neural Stem Cells

Abstract

SummaryHippocalcin (HPCA) is a calcium-binding protein that is restricted to nervous tissue and contributes to neuronal activity. Here we report that, in addition to inducing neurogenesis, HPCA inhibits astrocytic differentiation of neural stem cells. It promotes neurogenesis by regulating protein kinase Cα (PKCα) activation by translocating to the membrane and binding to phosphoinositide-dependent protein kinase 1 (PDK1), which induces PKCα phosphorylation. We also found that phospholipase D1 (PLD1) is implicated in the HPCA-mediated neurogenesis pathway; this enzyme promotes dephosphorylation of signal transducer and activator of transcription 3 (STAT3[Y705]), which is necessary for astrocytic differentiation. Moreover, we found that the SH2-domain-containing tyrosine phosphatase 1 (SHP-1) acts upstream of STAT3. Importantly, this SHP-1-dependent STAT3-inhibitory mechanism is closely involved in neurogenesis and suppression of gliogenesis by HPCA. Taken together, these observations suggest that HPCA promotes neuronal differentiation through activation of the PKCα/PLD1 cascade followed by activation of SHP-1, which dephosphorylates STAT3(Y705), leading to inhibition of astrocytic differentiation.

MicroRNA-24-3p regulates neuronal differentiation by controlling hippocalcin expression

“…These results strongly indicate that HPCA is required for the neuronal differentiation of SH-SY5Y cells. This is supported by a previous study showing that HPCA plays an important role in neuronal differentiation in various cell types, including H19-7 cells [28] and cortical neural stem cells [16]. …”

“…Previously, we reported that HPCA is critical for neuronal differentiation and neurite outgrowth in multiple cell types [16, 28]. To investigate whether HPCA was implicated in neuronal differentiation, either control siRNA or HPCA siRNA were transiently transfected into SH-SY5Y cells, which were then allowed to differentiate for 7 days.…”

“…We have previously shown that HPCA promotes NeuroD expression, resulting in neurite outgrowth during differentiation of H19-7 cells [28]. Furthermore, our previous study demonstrated that HPCA promotes neurogenesis by regulating the PKCα/PKD1/PLD1/SHP-1/STAT3 pathway in neural stem cells [16]. However, the molecular mechanisms involved in the regulation of HPCA expression during neuronal differentiation have not been studied yet.…”

“…Therefore, miRNAs are key regulators of mammalian neurodevelopment and have been increasingly linked to neuronal differentiation and the translatability of mRNAs in neurons. Our previous study showed that HPCA expression was gradually increased during neuronal differentiation [16]. Therefore, we assumed that an miRNA would be associated with HPCA expression during neuronal differentiation.…”

“…Our previous study showed that HPCA increases NeuroD expression, resulting in neurite outgrowth during the differentiation of H19-7 cells [28]. Moreover, it was found to promote neuronal differentiation through activation of the PKCα/PLD1/SHP1 cascade, leading to the inhibition of astrocytic differentiation in cortical neural stem cells [16]. We also reported that HPCA stimulates astrocytic differentiation through the activation of STAT3 in hippocampal neural precursor cells [29].…”