TY - JOUR
T1 - Expression of the p16INK4A/Cdkn2a gene is prevalently downregulated in human pheochromocytoma tumor specimens
AU - Muscarella, Peter
AU - Bloomston, Mark
AU - Brewer, Alexander R.
AU - Mahajan, Anjali
AU - Frankel, Wendy L.
AU - Ellison, E. Christopher
AU - Farrar, William B.
AU - Weghorst, Christopher M.
AU - Li, Junan
PY - 2008
Y1 - 2008
N2 - A number of hereditary syndromes have been found to be associated with pheochromocytoma development, but there is a paucity of data regarding secondary molecular events, such as downregulation of the p16INK4A/Cdkn2a gene (hereafter p16), contributing to pheochromocytoma tumorigenesis. Using tissue microarray and immunohistochemistry, we evaluated the expression of p16 in 31 pheochromocytoma tumor specimens. Our results showed that the p16 gene was expressed at low level or even not expressed in all but one specimens [30/31 (96.8%)], indicative of the prevalence of p16 downregulation in pheochromocytomas. In contrast, high expression of p16 was observed in the majority of control "normal" specimens [5/ 7 (71.6%)]. To further investigate the molecular mechanisms underlying p16 downregulation in pheochromocytomas, we used quantitative real-time PCR, methylation-specific PCR, and direct DNA sequencing to analyze these specimens for potential genetic alterations of the p16 gene. Deletions and aberrant CpG methylation of p16 were identified in 9 (29.0%) and 11 (35.5%) specimens, respectively, while one specimen harbored a point mutation, Ala → Pro at residue 20 of P16, and this mutation led to an eightfold decrease in the CDK4-inhibitory activity of P16. The overall frequency of p16 genetic alterations is 67.7%. Taken together, our results demonstrate that reduced expression of p16 is a common event in human pheochromocytomas, and the primary cause for such downregulation is inactivating genetic abnormalities in the p16 gene.
AB - A number of hereditary syndromes have been found to be associated with pheochromocytoma development, but there is a paucity of data regarding secondary molecular events, such as downregulation of the p16INK4A/Cdkn2a gene (hereafter p16), contributing to pheochromocytoma tumorigenesis. Using tissue microarray and immunohistochemistry, we evaluated the expression of p16 in 31 pheochromocytoma tumor specimens. Our results showed that the p16 gene was expressed at low level or even not expressed in all but one specimens [30/31 (96.8%)], indicative of the prevalence of p16 downregulation in pheochromocytomas. In contrast, high expression of p16 was observed in the majority of control "normal" specimens [5/ 7 (71.6%)]. To further investigate the molecular mechanisms underlying p16 downregulation in pheochromocytomas, we used quantitative real-time PCR, methylation-specific PCR, and direct DNA sequencing to analyze these specimens for potential genetic alterations of the p16 gene. Deletions and aberrant CpG methylation of p16 were identified in 9 (29.0%) and 11 (35.5%) specimens, respectively, while one specimen harbored a point mutation, Ala → Pro at residue 20 of P16, and this mutation led to an eightfold decrease in the CDK4-inhibitory activity of P16. The overall frequency of p16 genetic alterations is 67.7%. Taken together, our results demonstrate that reduced expression of p16 is a common event in human pheochromocytomas, and the primary cause for such downregulation is inactivating genetic abnormalities in the p16 gene.
KW - Expression downregulation
KW - Genetic alterations
KW - Pheochromocytomas
KW - p16
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U2 - 10.3727/105221608786883825
DO - 10.3727/105221608786883825
M3 - Article
C2 - 19110720
AN - SCOPUS:58149479433
SN - 1052-2166
VL - 14
SP - 207
EP - 216
JO - Gene expression
JF - Gene expression
IS - 4
ER -