Hodgkin's lymphoma cells express alternatively spliced forms of HDM2 with multiple effects on cell cycle control.
The HDM2 oncoprotein is a cellular inhibitor of p53 and is frequently deregulated in human cancer. However, the HDM2 gene encodes alternatively spliced variants whose functional significance is poorly understood. We had previously reported the detection of alternative HDM2 forms in Hodgkin's lymphoma (HL)-derived cell lines. Here, we have cloned several of these transcripts, including the previously described HDM2-A, -B and -C (which encode the COOH terminus of HDM2), and two novel variants (HDM2-HL1 and -HL2) containing a complete p53 interaction domain. Real-time PCR assays demonstrated that HDM2-A and -B were selectively expressed by HL cell lines and primary tumors, compared with their non-neoplastic counterparts. In transient transfection experiments, alternatively spliced HDM2 isoforms were partially or totally localized within the cytoplasm. HDM2-HL2 was able to inhibit transactivation of a p53-inducible reporter construct and induced a partial relocalization of p53 to the cytoplasm. Expression of HDM2-A and -B caused the activation of p53/p21 and induced growth arrest in primary cells, but also increased the expression levels of cyclins D1 and E. Other possible genes regulated by HDM2-A and -B were identified using cDNA microarray technology. These results imply that HDM2 isoforms may have multiple effects on cell cycle control, and provide insight into the mechanisms through which these molecules contribute to tumorigenesis.
Sánchez-Aguilera
A
A
Lymphoma Group, Molecular Pathology Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain. asanchez@cnio.es
García
J F
JF
Sánchez-Beato
M
M
Piris
M A
MA
D017398:Alternative Splicing; D002453:Cell Cycle; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006689:Hodgkin Disease / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008198:Lymph Nodes / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D020033:Protein Isoforms; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D016159:Tumor Suppressor Protein p53; D019938:Cyclin D1; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2