Activation of AKT and nuclear accumulation of wild type TP53 and MDM2 in anal squamous cell carcinoma

Abstract

Human papilloma virus (HPV) infection is considered as an important aetiological factor for anal squamous cell carcinoma (ASCC) but is not sufficient for tumour progression. This carcinoma is poorly understood at the molecular level. Using the largest cohort of cases to date we investigated the molecular mechanisms underlying ASCC development, in particular the roles of TP53, MDM2 and AKT. Viral infection in our cohort occured at high frequency (73%, 94/128) with HPV16 accounting for the majority (86%, 81/94) of infected cases. Only 4% (5/119) of ASCCs showed TP53 (exons 5-8) mutations, but a high frequency (91%, 100/110) of nuclear protein expression of TP53 was observed. There was a significant association (p < 0.001) between nuclear accumulation of TP53 and MDM2 protein although no MDM2 mutations were found, and copy number was normal. Cellular accumulation of phosphorylated-AKT was observed in 66% (82/ 125) of ASCCs and an association demonstrated between nuclear accumulation of MDM2 and activated AKT (p < 0.001). We observed a high frequency of copy number gain at PIK3CA (47%), and some coding sequence mutations (4%). Amplification of PIK3CA was associated with presence of phosphorylated-AKT (p 5 0.008). There was no association between virus infection and TP53 nuclear accumulation (p 5 0.5). However, a significant association was found between infection and MDM2 nuclear staining, and between infection and activated AKT (p 5 0.04, p 5 0.01, respectively). We propose that activation of AKT, possibly through the PI3K-AKT pathway, is an important component of ASCC tumorigenesis that contributes to MDM2 and TP53 accumulation in the nucleus. ' 2007 Wiley-Liss, Inc.Key words: anal cancer; TP53; MDM2; AKT; HPV; ASCC The annual incidence of anal squamous cell carcinoma (ASCC) is 1.4-2 per 100,000 in the general, heterosexual population and accounts for approximately 300 cases per year in the UK and 3,500 in the USA.1,2 Sexually transmitted infection with mucosal high-risk human papillomavirus (HPV) causes anal intraepithelial neoplasia, which may progress from low-grade through to highgrade and finally to invasive neoplasia. 3,4 This process has distinct parallels with cervical intraepithelial neoplasia, including, origin within squamous epithelium and infection with some viral subtypes, such as HPV type 16, which appear to confer a significant risk of malignant transformation.ASCC is poorly understood at the molecular level and it remains to be documented whether mutational pathways in ASCC reflect those seen in cervical neoplasia, or whether there are parallels with colorectal cancer. The most common genetic alteration in human cancer is mutation of the TP53 tumour suppressor gene. To date, mutation of TP53 in ASCC has been examined in a single study that investigated only 9 tumours and found 3 coding sequence mutations.5 Whilst the frequency of TP53 mutation needs to be clarified, nuclear accumulation of TP53 protein has been shown in 37-71% of anal tumours. 6-8 Whether wild type or mutant TP53 protein can accou...

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“…Methylation of several genes [59], human papilloma virus (HPV), p53, and AKT have been implicated in carcinogenesis of anal carcinoma [60]. Nilsson et al [61].…”

Phase II Study of Capecitabine in Substitution of 5-FU in the Chemoradiotherapy Regimen for Patients with Localized Squamous Cell Carcinoma of the Anal Canal

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Frequent mutations and amplifications of the PIK3CA gene in pituitary tumors

“…Two PIK3CA mutational 'hotspots' were found in exons 9 and 20 and activating mutations in these regions were seen in many human cancers , Hayes et al 2006, Karakas et al 2006, Kozaki et al 2006, Phillips et al 2006, Qiu et al 2008, Santarpia et al 2008. Genetic amplification of the PIK3CA gene was also seen in many tumors, including ovarian cancer (Shayesteh et al 1999), cervical cancer (Ma et al 2000), brain tumors (Hui et al 2001), non-small cell lung cancer (Massion et al 2002), squamous cell carcinoma (Woenckhaus et al 2002), gastric carcinoma (Byun et al 2003), esophageal adenocarcinoma (Miller et al 2003), thyroid tumors (Wu et al 2005), oral squamous cell carcinoma (Kozaki et al 2006), head and neck squamous cell carcinoma , and anal squamous cell carcinoma (Patel et al 2007). Genetic amplifications of the PIK3CA gene were associated with increased PIK3CA expression, PI3K activity, and phosphorylation and activation of AKT (Shayesteh et al 1999, Ma et al 2000, Massion et al 2002, Byun et al 2003, Wu et al 2005, Kozaki et al 2006.…”