Crucial roles for protein kinase C isoforms in tumor-specific killing by apoptin

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• Apoptin, derived from chicken anemia virus, selectively induces apoptosis in malignant and transformed cells, sparing normal cells.
• The precise mechanisms underlying apoptin's selective cytotoxicity remain incompletely understood.
• Understanding these mechanisms is crucial for therapeutic applications.

Purpose of the Study:

• To elucidate the molecular mechanisms of apoptin's selective cell killing.
• To investigate the role of protein kinases in apoptin activation and function.
• To explore the potential of apoptin for purging malignant cells in hematopoietic stem cell transplantation.

Main Methods:

• Development of a lentiviral vector (LV-GFP-AP) for efficient apoptin delivery into hematopoietic cells.
• Assessment of apoptin's cytotoxicity against various human leukemia and multiple myeloma cell lines, as well as normal CD34(+) cells.
• Expression array profiling to identify differential kinase expression between sensitive and resistant cell lines.
• Immunoprecipitation and in vitro kinase assays to identify and validate protein kinase C beta (PKCβ) as a key regulator of apoptin phosphorylation.
• RNA interference (shRNA) and drug-mediated inhibition to confirm the role of PKCβ.
• Analysis of downstream signaling pathways, including caspase activation and kinase regulation.

Main Results:

• Apoptin selectively killed multiple myeloma and leukemia cell lines, while sparing normal CD34(+) cells.
• Dexamethasone-resistant MM1.R cells showed increased susceptibility to apoptin, correlating with enhanced apoptin phosphorylation.
• Protein kinase C beta (PKCβ) was identified as a crucial kinase responsible for apoptin phosphorylation and activation.
• Inhibition of PKCβ significantly reduced apoptin phosphorylation and subsequent cell death.
• Apoptin-induced cell death involved the upregulation of PKCβ, activation of caspase-9/3, cleavage of PKCδ, and downregulation of MERTK and AKT.

Conclusions:

• A novel pathway for apoptin activation involving PKCβ and PKCδ has been elucidated.
• PKCβ plays a critical role in phosphorylating and activating apoptin.
• Apoptin-mediated cell death involves a complex signaling cascade including caspases and other kinases.
• These findings highlight the therapeutic potential of apoptin and its regulators for purging malignant cells in autologous bone marrow transplantation for multiple myeloma.