The parafibromin tumor suppressor protein inhibits cell proliferation by repression of the c-myc proto-oncogene

Parafibromin is a tumor suppressor protein encoded by HRPT2, a gene recently implicated in the hereditary hyperparathyroidism–jaw tumor syndrome, parathyroid cancer, and a subset of kindreds with familial isolated hyperparathyroidism. Human parafibromin binds to RNA polymerase II as part of a PAF1 transcriptional regulatory complex. The physiologic targets of parafibromin and the mechanism by which its loss of function can lead to neoplastic transformation are poorly understood. We show here that RNA interference with the expression of parafibromin or Paf1 stimulates cell proliferation and increases levels of the c-myc proto-oncogene product, a DNA-binding protein and established regulator of cell growth. This effect results from both c-myc protein stabilization and activation of the c-myc promoter, without alleviation of the c-myc transcriptional pause. Chromatin immunoprecipitation demonstrates the occupancy of the c-myc promoter by parafibromin and other PAF1 complex subunits in native cells. Knockdown of c-myc blocks the proliferative effect of RNA interference with parafibromin or Paf1 expression. These experiments provide a previously uncharacterized mechanism for the anti-proliferative action of the parafibromin tumor suppressor protein resulting from PAF1 complex-mediated inhibition of the c-myc proto-oncogene.

[1]  W. Simonds,et al.  Nuclear Localization of the Parafibromin Tumor Suppressor Protein Implicated in the Hyperparathyroidism-Jaw Tumor Syndrome Enhances Its Proapoptotic Function , 2007, Molecular Cancer Research.

[2]  J. Nevins,et al.  Ras enhances Myc protein stability. , 1999, Molecular cell.

[3]  J. Carpten,et al.  Somatic and germ-line mutations of the HRPT2 gene in sporadic parathyroid carcinoma. , 2003, The New England journal of medicine.

[4]  G. Hendy,et al.  Influence of calcium and 1,25-dihydroxycholecalciferol on proliferation and proto-oncogene expression in primary cultures of bovine parathyroid cells. , 1989, Endocrinology.

[5]  J. Testa,et al.  Perturbations of the AKT signaling pathway in human cancer , 2005, Oncogene.

[6]  K Hammje,et al.  HRPT2 mutations are associated with malignancy in sporadic parathyroid tumours , 2003, Journal of medical genetics.

[7]  J. Carpten,et al.  Hyperparathyroidism‐jaw tumour syndrome , 2003, Journal of internal medicine.

[8]  K. Basler,et al.  Parafibromin/Hyrax Activates Wnt/Wg Target Gene Transcription by Direct Association with β-catenin/Armadillo , 2006, Cell.

[9]  B. Harding,et al.  Parafibromin mutations in hereditary hyperparathyroidism syndromes and parathyroid tumours , 2006, Clinical endocrinology.

[10]  M. Gstaiger,et al.  The HRPT2 Tumor Suppressor Gene Product Parafibromin Associates with Human PAF1 and RNA Polymerase II , 2005, Molecular and Cellular Biology.

[11]  T. Sano,et al.  Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism–jaw tumour syndrome , 2006, Clinical endocrinology.

[12]  M. Rosner,et al.  Ras mediates cell survival by regulating tuberin , 2008, Oncogene.

[13]  J. Carpten,et al.  Germline and de novo mutations in the HRPT2 tumour suppressor gene in familial isolated hyperparathyroidism (FIHP) , 2004, Journal of Medical Genetics.

[14]  W. Simonds,et al.  Parafibromin, product of the hyperparathyroidism-jaw tumor syndrome gene HRPT2, regulates cyclin D1/PRAD1 expression , 2005, Oncogene.

[15]  J. Moore,et al.  c-myc protein expression in untransformed fibroblasts. , 1991, Oncogene.

[16]  O. Rozenblatt-Rosen,et al.  The Parafibromin Tumor Suppressor Protein Is Part of a Human Paf1 Complex , 2005, Molecular and Cellular Biology.

[17]  M. Groudine,et al.  The block to transcriptional elongation within the human c-myc gene is determined in the promoter-proximal region. , 1992, Genes & development.

[18]  W. Simonds,et al.  Surveillance for Early Detection of Aggressive Parathyroid Disease: Carcinoma and Atypical Adenoma in Familial Isolated Hyperparathyroidism Associated With a Germline HRPT2 Mutation , 2006, Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research.

[19]  G. Åkerström,et al.  Accumulation of nonphosphorylated beta-catenin and c-myc in primary and uremic secondary hyperparathyroid tumors. , 2007, The Journal of clinical endocrinology and metabolism.

[20]  Paul Tempst,et al.  The human PAF complex coordinates transcription with events downstream of RNA synthesis. , 2005, Genes & development.

[21]  J. Carpten,et al.  Familial isolated hyperparathyroidism is rarely caused by germline mutation in HRPT2, the gene for the hyperparathyroidism-jaw tumor syndrome. , 2004, The Journal of clinical endocrinology and metabolism.

[22]  B. Teh,et al.  Parafibromin inhibits cancer cell growth and causes G1 phase arrest. , 2006, Biochemical and biophysical research communications.

[23]  Weili Ma,et al.  p53-Dependent Transcriptional Repression of c-myc Is Required for G1 Cell Cycle Arrest , 2005, Molecular and Cellular Biology.

[24]  D. Reinberg,et al.  Histone H2B Monoubiquitination Functions Cooperatively with FACT to Regulate Elongation by RNA Polymerase II , 2006, Cell.

[25]  D. Kimelman.  Faculty Opinions recommendation of Parafibromin/Hyrax activates Wnt/Wg target gene transcription by direct association with beta-catenin/Armadillo. , 2006 .

[26]  R. Norum,et al.  Hereditary hyperparathyroidism and multiple ossifying jaw fibromas: a clinically and genetically distinct syndrome. , 1990, Surgery.

[27]  M. Bisceglia,et al.  Diagnosis of parathyroid tumors in familial isolated hyperparathyroidism with HRPT2 mutation: implications for cancer surveillance. , 2006, The Journal of clinical endocrinology and metabolism.

[28]  T. Kerppola,et al.  Intrinsic sites of transcription termination and pausing in the c-myc gene , 1988, Molecular and cellular biology.

[29]  J. Carpten,et al.  HRPT2, encoding parafibromin, is mutated in hyperparathyroidism–jaw tumor syndrome , 2002, Nature Genetics.

[30]  C. Marcocci,et al.  Genetic analyses of the HRPT2 gene in primary hyperparathyroidism: germline and somatic mutations in familial and sporadic parathyroid tumors. , 2004, The Journal of clinical endocrinology and metabolism.