[Biallelic mutation of SOCS-1 impairs JAK2 degradation and sustains phospho-JAK2 action in MedB-1 mediastinal lymphoma line].
Primary mediastinal B-cell lymphoma (PMBL) is a well-defined subtype of diffuse large B-cell lymphoma. Molecular cytogenetics revealed frequent gains of 9 p24. JAK2, mapping in this region, is presently regarded as a candidate oncogene since expression profiling showed high JAK2 transcript levels and JAK2 was found to be constitutively phosphorylated in mediastinal B-cell lymphomas. We confirm that in the MedB-1 mediastinal B-cell line, harbouring a trisomy 9, JAK2 transcription is elevated and the product is highly phosphorylated. However, JAK2 is not over-expressed at the protein level. On top, JAK2 protein turnover is even delayed. This unexpected finding coincides with a biallelic mutation of the SOCS-1 gene in this cell, which abrogates SOCS box function of the protein. Ectopic expression of wt-SOCS-1 in MedB-1 leads to growth arrest, dramatic reduction of phospho-JAK2 and its downstream partner phospho-STAT5. We conclude that, in MedB-1, action of phospho-JAK2 is sustained due to defective SOCS-1. Hence, SOCS-1 qualifies as a novel tumor suppressor. Of note, the SOCS-1 mutations are also present in the parental tumor of MedB-1 and were detected in 9 of 20 PMBL.
Department of Pathology, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm. thomas.barth@medizin.uni-ulm.de
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Barth
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Melzner
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Wegener
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Bucur
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Brüderlein
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Dorsch
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Hasel
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Leithäuser
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Möller
D002899:Chromosomes, Human, Pair 9; D004252:DNA Mutational Analysis; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053614:Janus Kinase 2 / Q000235:genetics / Q000378:metabolism*; D016393:Lymphoma, B-Cell / Q000235:genetics*; D008479:Mediastinal Neoplasms / Q000235:genetics*; D009154:Mutation; D010766:Phosphorylation; D011230:Precancerous Conditions / Q000235:genetics; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics*; D014158:Transcription, Genetic; D014314:Trisomy
C108944:SOCS1 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C507924:JAK2 protein, human; D053614:Janus Kinase 2