Multiple subcellular localizations and functions of protein kinase Cδ in liver cancer

TLR Engagement Induces an Alternate Pathway for BCR Signaling that Results in PKCδ Phosphorylation

Recently, we reported that preexposure of B cells to IL-4 induced an alternate, signalosome-independent BCR signaling pathway leading to protein kinase C (PKC)δ phosphorylation (pTyr311), which occurs in the membrane compartment. This is considered to represent a form of receptor crosstalk and signal integration. Unlike the classical BCR signaling pathway, Lyn kinase is indispensable for BCR-induced downstream events in the alternate pathway. Our previous report that alternate BCR signaling leading to ERK phosphorylation is triggered by LPS and PAM3CSK4 (much like IL-4) raises the possibility that other signaling outcomes such as PKCδ phosphorylation might be similarly affected. To explore the range of mediators capable of producing an alternate pathway for BCR signaling, we examined PKCδ translocation and phosphorylation in LPS- and PAM3CSK4-treated B cells stimulated by anti-Ig. We found that LPS and PAM3CSK4 alter the signaling pathway used by the BCR to produce PKCδ phosphorylation. As with IL-4, elements of the signalosome are not needed for PKCδ phosphorylation when BCR triggering occurs after LPS and PAM3CSK4. However, with LPS and PAM3CSK4, anti-Ig-induced phosphorylation of PKCδ takes place in the cytosol, in contrast to the IL-4-induced alternate pathway, wherein PKCδ phosphorylation occurs in the membrane. Furthermore, the BCR signaling pathway induced by LPS and PAM3CSK4 differs from that induced by IL-4 by not requiring Lyn. Thus, an alternate, signalosome-independent BCR signaling pathway for PKCδ phosphorylation is induced by TLR agonists but differs in important ways from the alternate pathway induced by IL-4.

Inhibition of Calcium-Sensing Receptor Alleviates Chronic Intermittent Hypoxia-Induced Cognitive Dysfunction via CaSR-PKC-ERK1/2 Pathway

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is typically characterized by chronic intermittent hypoxia (CIH), associated with cognitive dysfunction in children. Calcium-sensing receptor (CaSR) mediates the apoptosis of hippocampal neurons in various diseases. However, the effect of CaSR on OSAHS remains elusive. In the present study, we investigated the role of CaSR in CIH-induced memory dysfunction and underlying mechanisms on regulation of PKC-ERK1/2 signaling pathway in vivo and in vitro. CIH exposures for 4 weeks in mice, modeling OSAHS, contributed to cognitive dysfunction. CIH accelerated apoptosis of hippocampal neurons and resulted in the synaptic plasticity deficit via downregulated synaptophysin (Syn) protein level. The mice were intraperitoneally injected with CaSR inhibitor (NPS2143) 30 min before CIH exposure and the results demonstrated CaSR inhibitor alleviated the apoptosis and synaptic plasticity deficit in the hippocampus of CIH mice. We established intermittent hypoxia PC12 cell model and found that the activation of CaSR accelerated CIH-induced PC12 apoptosis and synaptic plasticity deficit by upregulated p-ERK1/2 and PKC. Overall, our findings revealed that CaSR held a critical function on CIH-induced cognitive dysfunction in mice by accelerating hippocampal neuronal apoptosis and reducing synaptic plasticity via augmenting CaSR-PKC-ERK1/2 pathway; otherwise, inhibition of CaSR alleviated CIH-induced cognitive dysfunction.

Microtubule-affinity regulating kinase 4: A potential drug target for cancer therapy

The human genome encodes more than 500 protein kinases that work by transferring the γ-phosphate group from ATP to serine, threonine, or tyrosine (Ser/Thr/Tyr) residues. Various kinases are associated with the onset of cancer and its further progression. The recent advancements in developing small-molecule kinase inhibitors to treat different cancer types have shown noticeable results in clinical therapies. Microtubule-affinity regulating kinase 4 (MARK-4) is a Ser/Thr protein kinase that relates structurally to AMPK/Snf1 subfamily of the CaMK kinases. The protein kinase modulates major signalling pathways such as NF-κB, mTOR and the Hippo-signalling pathway. MARK4 is associated with various cancer types due to its important role in regulating microtubule dynamics and subsequent cell division. Aberrant expression of MARK4 is linked with several pathologies such as cancer, Alzheimer's disease, obesity, etc. This review provides detailed information on structural aspects of MARK4 and its role in various signalling pathways related to cancer. Several therapeutic molecules were designed to inhibit the MARK4 activity from controlling associated diseases. The review further highlights kinase-targeted drug discovery and development in oncology and cancer therapies. Finally, we summarize the latest findings regarding the role of MARK4 in cancer, diabetes, and neurodegenerative disease path to provide a solid rationale for future investigation and therapeutic intervention.