A novel role for the phosphatidylinositol-4,5-bisphosphate 3-kinase delta isoform in hepatocellular proliferation

The phosphatidylinositol-4,5-bisphosphate 3-kinase delta isoform (Pik3cd), usually considered immune-specific, was unexpectedly identified as a gene potentially related to either regeneration and/or differentiation in animals lacking hepatocellular Integrin Linked Kinase (ILK). Since a specific inhibitor (Idelalisib, or CAL101) for the catalytic subunit encoded by Pik3cd (p110δ) has reported hepatotoxicity when used for treating Chronic Lymphocytic Leukemia and other lymphomas, we aimed to elucidate if there is a role for p110δ in normal liver function. To determine the effect on normal liver regeneration, partial hepatectomy (PHx) was performed using mice in which p110δ was first inhibited using CAL101. Inhibition led to over a 50% decrease in proliferating hepatocytes in the first two days after PHx. This difference correlated with phosphorylation changes in the HGF and EGF receptors (MET and EGFR, respectively) and NF-κB signaling. Ingenuity Pathway Analyses implicated C/EBPβ, HGF and the EGFR heterodimeric partner, ERBB2, as three of the top 20 regulators downstream of p110δ signaling as their pathways were suppressed in the presence of CAL101 at one day post-PHx. A regulatory role for p110δ signaling in mouse and rat hepatocytes through MET and EGFR was further verified using hepatocyte primary cultures, in the presence or absence of CAL101. Combined, this data supports a role for p110δ as a downstream regulator of normal hepatocytes when stimulated to proliferate.