Leukocyte Specific Protein‐1 (LSP1) Functions as a Suppressor of Proliferation During Liver Regeneration After Partial Hepatectomy (PHx) and in Primary Hepatocytes

Abstract

Leukocyte specific protein‐1 (LSP1), an f‐actin binding protein expressed in hematopoietic cells and hepatocytes, is the gene with the highest copy number variation in human hepatocellular carcinoma. Our previous work has demonstrated that loss of LSP1 expression leads to increased proliferation and migration of rat hepatocellular carcinoma cells. We have also demonstrated that overexpression of LSP1 in mouse liver through hydrodynamic tail vein injection of LSP1 plasmid DNA results in a significant decrease in proliferation on day 2 after partial hepatectomy (PHx). To further characterize the role of LSP1 in liver regeneration, we performed 2/3 PHx on both a global LSP1 knockout mouse as well as a hepatocyte specific LSP1 transgenic mouse model and analyzed proliferation using ki67 immunohistochemistry as well as western blot analysis of ERK signaling. Since expression of LSP1 leads to decreased proliferation, we hypothesized that the knockout mouse model would exhibit increased proliferation and activation of ERK whereas the transgenic mouse model would display decreased proliferation and pERK expression. LSP1 knockout mice displayed an increase in Ki67 labeling on day 4 after PHx and western blot analysis shows increased pERK expression after PHx in comparison to controls. In the transgenic mouse model, a significant decrease in Ki67 positive hepatocytes was observed on day 4 after PHx as well as decreased pERK expression. Transgenic mice also displayed decreased liver to body weight ratios on day 7 following PHx. Hepatocytes isolated from knockout mice exhibited increased proliferation in the absence of growth factors compared to controls whereas transgenic mouse hepatocytes displayed decreased BrdU incorporation in both the presence and absence of growth factors. LSP1 knockout hepatocytes and transgenic hepatocytes also displayed increased and decreased pERK expression, respectively. Our results demonstrate that LSP1 functions as an inhibitor of proliferation in primary hepatocytes as well as during liver regeneration following PHx. Future studies aim to address the signaling pathways downstream of LSP1 that effect proliferation during liver regeneration as well as how LSP1 functions in hepatocarcinogenesis mechanisms and sensitivity to sorafenib.Support or Funding InformationMenten Endowment, University of Pittsburgh