Expression of retinoblastoma protein and P16 proteins in classic Hodgkin lymphoma: relationship with expression of p53 and presence of Epstein-Barr virus in the regulation of cell growth and death☆

Summary 

Deregulation of several genes involved in cell cycle control has been reported in classic Hodgkin lymphoma (cHL). This study aimed to investigate the expression of tumor suppressor proteins (P16^INK4A, retinoblastoma protein, and p53) in cHL in relation to the proliferation and apoptosis of Hodgkin/Reed-Sternberg (H/RS) cells, correlating with the status of Epstein-Barr virus (EBV). A total of 66 cHL cases and 10 nonneoplastic reactive lymphoid tissues were retrieved from the archives. Immunohistochemistry technique was used for the detection of protein expression. Presence of EBV infection was detected by EBV early RNA in situ hybridization. p16^INK4A gene deletion status was assessed by fluorescence in situ hybridization technique. Expression of P16^INK4A was observed in 49.2% of the cases, whereas positive retinoblastoma protein and p53 expressions in the H/RS cells were detected in 89.1% and 81.5% of the cases, respectively. Epstein-Barr virus positivity was detected in 53.0% of the cases. Proliferation marker, Ki-67 expression, was observed in 86.7% of the cases. There was no significant correlation between the expression of the various tumor suppressor proteins and Ki-67. Retinoblastoma protein and p53 were also not associated with the presence of EBV. An inverse relationship was observed between the expression of P16^INK4A and the presence of EBV. There were no significant homozygous or hemizygous deletions of the p16^INK4A gene. However, an aberrant copy number of chromosome 9 with the loss of one or more p16^INK4A loci was detected in all cases assessable by fluorescence in situ hybridization. Loss of function of one or more tumor suppressor proteins may be involved in defective cell regulation of H/RS cells. Epstein-Barr virus may have a role in inhibiting P16^INK4A expression, thus resulting in a perturbed p16^INK4A-Rb cell cycle checkpoint.

Keywords: Cell cycle control, Hodgkin lymphoma, P16^INK4A, PRb, p53