The significance of pre-S1 mutants as a cause of groundglass hepatocyte during HBV infection

Cho, Yong Kyun; Kim, Byung Ik; Pae, Ji Cheul; Park, Seung Ha; Kim, Sang Hoon; Park, Jung Ho; Kim, Hong Joo; Park, Dong Il; Kim, Hyang; Sung, In Kyung; Sohn, Chong Il; Jeon, Woo Kyu

Abstract

BACKGROUND: Ground glass hepatocytes are unique histological feature of chronic hepatitis B viral infection. The pre-S1 region of large surface protein has been shown to regulate assembly, processing, and secretion of HBsAg. The purpose of this study was to elucidate that a mutant form of pre-S1 affects this normal secretory pathway and is responsible for ground glass hepatocyte.
METHODS
We examined HBV sequences spanning the pre-S region from a patients with HBeAg positive chronic HBV infection. HBV DNA was extracted from serum, cloned, and sequenced and determined the intrahepatic viral composition by extracting HBV DNA from paraffin embedded liver tissue. To analyze the viral population of single groundglass hepatocytes, we used the technique of laser capture microdissection to isolate individual hepatocytes from biopsy specimen. Groundglass hepatocytes that stained positively with anti-HBs and normal hepatocytes were harvested individually and their subjected HBV DNA sequences were analyzed. To define the responsible mutations for the HBsAg secretion, we introduced the mutant gene into molecular clone of wildtype (adwR9) and assayed their HBsAg amounts in the transfected cell supernatants by ELISA.
RESULTS
Of 12 clones in serum analyzed, 9 clones had identical wild type sequences in the N-terminal region of the pre-S1 protein which plays an important role in the secretion and retention of HBV envelope proteins. One of the wild type clones has deletion within pre-S2 region. 3 identical mutant clones were isolated. Mutant type clones were predominant groundglass hepatocytes.
CONCLUSIONS
We speculate that a mutant form of the HBV pre-S1 protein may result in the formation of ground-glass hepatocytes. Expression of abnormal pre-S1 may lead to its retention and accumulation within hepatocytes.