Detection of Homozygous Deletions and Mutations in the CDKN2A Gene in Hydatidiform Moles

OBJECTIVE To investigate homozygous deletions and mutations in the CDKN2A gene(p16 INK4a and p14 ARF gene)in hydatidiform moles. METHODS A total of 38 hydatidiform mole samples and 30 villi samples were examined for homozygous deletions in the CDKN2A gene by PCR and for mutations by DHPLC. RESULTS i)Among 38 hydatidiform mole samples, homozygous deletions in the p16 INK4a exon 1 were identified in 5 cases(13.2%),while no homozygous deletions were found in the p16I NK4aexon 1 of 30 early-pregnancy samples.The rates of those deletions in hydatidiform compared to early-pregnancy villi samples was statistically significant(P=0.036).ii)No homozygous deletions in the p14 ARF exon 1 or p16 INK4a exon 2 were found in any of the hydatidiform moles or early-preganancy samples.iii) In all hydatidiform moles and early-pregnancy villi samples,no mutations were detected by DHPLC. CONCLUSION We suggest there may be a close correlation between homozygous deletions in the CDKN2A gene and occurrence of hydatidiform moles variation in the CDKN2A gene is mainly caused by homozygous deletions,while mutations may be not a major cause.

Two distinct pathways of p16 gene inactivation in gallbladder cancer

AIM: To examine the mechanism of inactivation of the p16 gene in gallbladder cancer,and to investigate p16 alterations and their correlation with clinicopathological features. METHODS: Specimens were collected surgically from 51 patients with gallbladder cancer. We evaluated the status of protein expression,loss of heterozygosity (LOH),homozygous deletion and promoter hypermethylation using immunohistochemistry,microsatellite analysis,quantitative real-time polymerase chain reaction (PCR) and methylation-specific PCR,respectively. In addition,mutations were examined by direct DNA sequencing. RESULTS: Homozygous deletions of the p16 gene exon2,LOH at 9p21-22,p16 promoter hypermethylation,and loss of p16 protein expression were detected in 26.0% (13/50),56.9% (29/51),72.5% (37/51) and 62.7% (32/51),respectively. No mutations were found. LOH at 9p21 correlated with the loss of p16 protein expression (P < 0.05). Homozygous deletion of the p16 gene,a combination LOH and promoter hypermethylation,and multiple LOH at 9p21 were significantly correlated with the loss of p16 protein expression (P < 0.05). LOH at 9p21 and promoter hypermethylation of the p16 gene were detected in 15.4% (2/13) and 92.3% (12/13) of the tumors with homozygous deletion of the p16 gene,respectively. P16 alterations were not associated with clinicopathological features. CONCLUSION: Our results suggest that LOH and homozygous deletion may be two distinct pathways in the inactivation of the p16 gene. Homozygous deletion,a combination of LOH and promoter hypermethylation,and multiple LOH are major mechanisms of p16 inactivation in gallbladder cancer.

Mutations in the p16 gene in DMBA-induced pancreatic intraepithelial neoplasia and pancreatic cancer in rats

BACKGROUND：7,12-dimethylbenzanthracene（DMBA）-induced pancreatic intraepithelial neoplasia（PanIN）and pancreatic cancer in rats provide a classic model for uncovering the molecular mechanisms underlying pancreatic cancer.However,this model has not been characterized genetically,and in particular,the major genetic alterations in the p16 gene are unknown.METHODS： Lesions of PanlN and pancreatic cancer were induced with DMBA implantation in 40 rats, and control pancreatic tissue was obtained from 10 age-matched rats without exposure to DMBA. Pancreatic tissue was harvested three months after DMBA implantation and DNA was extracted. Homozy- gous deletions and point mutations of the pl6 （exons 1 and 2） gene were detected by PCR amplification and direct sequencing. RESULTS： DMBA implantation in the 40 rats induced 26 Pan- INs and 9 carcinomas. The overall frequency of p 16 alterations in the pancreatic tissue of these rats was 42.86% （15/35）, and the changes were point mutations, not homozygous deletions. p16 mutations were present in 30.77% （8/26） of the rats with PanIN and 77.78% （7/9） of the rats with carcinoma （P〈0.05）. The increasing incidence of p16 alterations was detected in 20.00% （1/5） of PanIN-1, 28.57% （2/7） of PanIN-2 and 35.71% （5/14） of PanIN-3 lesions. CONCLUSION： Our findings indicated that p16 alteration is a common event in the carcinogenesis of this model and that the mutation pattern is analogous to that of human lesions.

INACTIVATION OF P16 GENE IN LEUKEMIA

To determine the frequency of p16 gene inactivation in leukemia cells, and to evaluate their value in the prediction of their clinical outcome. Bone marrow or peripheral blood samples from 48 patients with leukemia were examined by multiplex polymerase chain reaction(MPCR) to detect p16 gene homozygous deletion, and restriction enzyme PCR to detect p16 gene methylation. p16 gene inactivation were detected in 10 of the 48 patients(20.4%). They were five patients with p16 homozygous deletion, and five patients with p16 methylation, respectively. p16 gene inactivation correlates with adverse prognosis features. The patients with p16 inactivation had poor response to chemotherapy, and had significantly shorter survival times than the patients in whom p16 gene was preserved(P<0.001). The inactivation of p16 gene play a key role in the pathogenesis and the progression of some leukemia. The detection of p16 gene is reliable prognostic factor that predict shortened survival times.