Analysis of the p16^INK4A, p15^INK4B and p18^INK4C genes in multiple myeloma

Abstract

Summary.To study the structural integrity of the cyclindependent kinase inhibitors known as INK4A (p16), INK4B (p15) and INK4C (p18) in multiple myeloma, we examined 20 primary myeloma samples (including one case of plasma cell leukaemia) using polymerase chain reaction-single strand conformation polymorphism, and 17 samples were examined by Southern blot analysis. The plasma cell leukaemia sample had homozygous deletions of the p15 and p16 genes (6%). One myeloma case had a p15 gene homozygous deletion (6%) with an intact p16 gene. This sample also had a p18 homozygous deletion, suggesting that the deletion of both genes may be important in either the development or progression of myeloma. No point mutations of these INK4 genes were found in the 20 samples. This is the first report that indicates that deletions of p15, p16 and p18 genes occur in some individuals with multiple myeloma (2/17 cases).

Frequent inactivation of the cyclin-dependent kinase inhibitor p18 by homozygous deletion in multiple myeloma cell lines: ectopic p18 expression inhibits growth and induces apoptosis

“…Some of these deletions coexisted with hemizygous p16 deletion and suggest a selection advantage for concomitant cyclin D1 overexpression and deletion of one or more CDK inhibitors, potentially contributing to cell transformation and enhanced cell proliferation. p18 gene deletions and rearrangements have been identified in MCL and MM 21,28,29 but not in other neoplasms, [22][23][24][25][26][27] supporting a possible role of this CDKI in MCL and myeloma pathogenesis. At this point, it is unknown whether p18 deletions in MM tumor cell lines represent an epiphenomenon of the cell culture process, although there is a report of such deletion in primary MM and in childhood T cell ALL samples.…”

“…At this point, it is unknown whether p18 deletions in MM tumor cell lines represent an epiphenomenon of the cell culture process, although there is a report of such deletion in primary MM and in childhood T cell ALL samples. 21,26 It is also unknown whether additional loss-offunction mutations including gene hypermethylation or point mutations are operative in MM or other human malignancies; p18 was inactivated by a point mutation in BT-20 human breast cancer cells rendering it deficient in suppressing cell growth. 32 In view of the high frequency of p18 deletions in MM cell lines, we investigated the significance of p18 inactivation by replacing its biologic function in a human myeloma cell line.…”

“…21 The p18 gene has been mapped to human chromosome 1p32. Although p18 deletions have been reported to be rare in human malignancy, [22][23][24][25][26][27] cytogenic analysis has shown abnormalities of 1p32-36 in 16% of human MM as well as 14% of low-grade non-Hodgkin's lymphoma (NHL) and 12% of diffuse large cell lymphoma.…”

“…PCR amplification of p18 exon 1 generated a clear band in cells with wild-type p18, whereas homozygous deletions were found in the cell lines KMS12, MM1, MY5, OPM2 (Figure 1b) and SKMM2 (data not shown). As p18 deletions are rare in most human neoplasms and cell lines [22][23][24][25][26][27] but have been identified in mantle cell lymphoma and some human myelomas, 21,28,29 these frequent deletions in MM cell lines suggest a pathogenic role via cell cycle dysregulation, either alone or in concert with cyclin D1 overexpression.…”

Hypermethylation of p16INK4A gene promoter during the progression of plasma cell dyscrasia

“…4,5,7 However, such alterations have seldom been found in MM despite its status as a lymphoid malignancy. 8,9 DNA methylation of CpG islands in the promoter region is known to lead to epigenetic gene inactivation by transcriptional silencing. 10 DNA methylation normally occurs in selected imprinted genes 11 and genes on the inactive X-chromosome of females, 12 and may play an important role during normal embryonic development.…”