The Function and Autophagy Regulation of PLEKHA8 in T Cell Acute Lymphoblastic Leukemia

Introduction:T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy. Over the past 20 years, several oncogenic drivers and crucial signaling pathways have been unraveled in this disease. However, most T-ALL patients are still treated with high dose multiagent chemotherapy due to limited targeted treatment. To further investigate the pathogenesis and develop the new therapeutic targets of T-ALL, we previously developed a mouse genetic model of T-ALL that is deficient forPtentumor suppressor gene. We identified PLEKHA8, a Golgi protein, is highly expressed in thePtenconditional knockout mouse T-ALL. We have verified the high expression of PLEKHA8 in patients' T-ALL samples. PLEKHA8 has the pleckstrin homology (PH) domain binding to phosphatidylinositol 4-monophosphate (PI4P) at the Golgi, is important in lipid metabolism and transport. The Golgi complex regulates the production and delivery of proteins and lipids, and is a site of lipid metabolism needed for autophagy, in particular PI(4)P. We hypothesized that PLEKHA8 affects the cell function and plays a role in the autophagy of human T-ALL via lipid metabolism.

Methods:PLEKHA8 was knocked down in T-ALL cell lines using a lentivirus-based vector with shRNAs to assess its effect on cell function. CCK8 assay was employed to detect the cell proliferation. Cell cycle was analyzed using 5-bromo-2'-deoxyuridine (BrdU) and flow cytometry. Autophagy proteins were monitored by western blot. PI(4)P was tested by confocal fluorescence microscopy.

Results:T-ALL cells underwent lower cell proliferation and sub-G1 cell accumulation after knocking down PLEKHA8 gene by using shRNA systems. The autophagy marker LC3, Beclin 1 and ATG 5 were markedly increased while P62 decreased after the downregulation PLEKHA8 in T-ALL cells. In addition, PLEKHA8 knocking down in T-ALL cells led to the accumulation of PI(4)P in cytoplasm as observed by confocal fluorescence microscopy.

Conclusion:Our data indicate that PLEKHA8 facilitates cell growth in T-ALL cells. Decreased expression of PLEKHA8 inhibits cell proliferation and accumulate sub-G1 phase of T-ALL cells. Decreased PLEKHA8 expression increases the autophagy of T-ALL cells, which could be based on the PI(4)P pathway of autophagy. Our studies provide a new insight into the pathogenesis and potential targeted therapy of T-ALL.