The development of human
cancers is frequently associated with the silencing of the two major
tumor suppressor pathways represented by
retinoblastoma protein and p53. As the incidence of p53 mutations is significantly lower in
Hodgkin's lymphoma than in other
neoplasias, we investigated whether the malfunction of other
proteins in this pathway could be responsible for its inactivation. Because the existence of nucleolar complexes between
p14(ARF) and Hdm2 has been described as having a critical effect on p53 function by inhibiting its degradation, we analyzed the expression and subcellular localization of these
proteins in 52 cases and in Hodgkin's cell lines. Two of four cell lines revealed loss of
p14(ARF) expression secondary to gene promoter methylation, this being mutually exclusive with p53 mutations (1 of 4), illustrating the existence of selective pressure to inactivate the p53 pathway. The majority of Hodgkin's samples showed a strong nucleolar expression of
p14(ARF) that was not associated with Hdm2. They also showed the existence of Hdm2/p53 complexes, and the absence of complexes containing either
p14(ARF)/Hdm2 or
p14(ARF)/p53. The different localization of Hdm2 (nucleoplasm) and
p14(ARF) (nucleoli) observed in Hodgkin's
tumors and cell lines is associated with the presence of short alternatively spliced transcripts of Hdm2 lacking the ARF-binding region and the
nuclear export signal. The absence of these
p14(ARF)/Hdm2 nucleolar complexes could be sufficient to inactivate the pathway and may explain the low frequency of p53 mutations in this
tumor.