A subset of head and neck squamous cell carcinomas exhibits integration of HPV 16/18 DNA and overexpression of p16^INK4A and p53 in the absence of mutations in p53 exons 5–8

Abstract

Head and neck squamous cell carcinomas (HNSCC) account for 6.5% of annual cancer cases worldwide. During the last decades, the incidence of HNSCC has increased in Western Europe. For example, the incidence of cancer of the mouth and pharynx increased from 26.8 to 33.8 per 100,000 from 1985 to 1990. 1,2 Recent data suggest that this increase in incidence is especially high in patients younger than 40 years of age. 3,4 Median age at presentation of HNSCC is 60 years, and 66.7% of the patients are men.Tobacco smoking, alcohol drinking and betel quid chewing are well-known risk factors in the etiology of HNSCC, responsible for 90% of the cases. 5,6 The age at smoking initiation appears to be inversely associated with a higher relative risk of developing a carcinoma. 5,7 Tobacco and alcohol use are independent risk factors, but when combined a synergistic effect is observed. 5 In addition, epidemiologic and molecular data suggest that human oncogenic papillomaviruses (HPVs), known to cause cervical and other anogenital cancers, may also promote head and neck carcinogenesis. 8 -10 Discrepancy exists with respect to the percentage of HNSCC harboring HPV, as the reported frequencies in head and neck lesions vary over a wide range (2-76%). 8,11 These differences may be due to the detection method used (Southern blot hybridization, polymerase chain reaction (PCR) or in situ hybridization), the anatomic location of tumors, the type of HPV detected and/or the number of tissue samples analyzed in the various studies. 8,11 Most studies have so far concentrated on the role of HPV in the etiology of uterine cervical cancer. 12 Particularly the high-risk oncogenic HPVs, such as HPV type 16 and 18, induce preneoplastic lesions with an increased risk of progression to cancer. The transition from dysplasia to invasive cancer appears to be associated with integration of the viral DNA into the host genome, most probably at fragile sites in chromosomes. [13][14][15] Molecular studies have shown that HPV integration results in upregulation of the viral oncoproteins E6 and E7. 8,12 The E6 protein contains zincbinding motifs and can complex with the host cell p53, thereby inducing p53 degradation through the ubiquitin-mediated pathway and thus preventing a cell cycle block and induction of apoptosis in DNA-damaged cells. The E7 protein forms complexes with hypophosphorylated forms of the retinoblastoma tumor suppressor protein (pRb), resulting in a decrease of the cellular pRb level and a release of E2F, a transcription factor involved in cell cycle progression. 16,17 Since HPV inactivates both p53 and pRb, it is expected that inactivating mutations in these genes do not play an important role in HPV-infected HNSCC. This is not only the case in cervical cancers 10,12 but also in half of the HNSCC. 6 Some studies on HNSCC, however, have reported the concomitant presence of HPV DNA and p53 overexpression and/or mutation. 9,18 -21 This gives rise to the question as to whether HPV is causally related to the development of a subgroup of HN...

P21Cip1/WAF1 expression is strongly associated with HPV-positive tonsillar carcinoma and a favorable prognosis

“…We noticed that the tumors with the low expression levels of pRb showed the overexpression of p16 INK4A . Accumulation of this latter protein has been strongly associated with the presence of oncogenic HPV in oropharyngeal carcinomas, 7,10,14,15 which was also evident in the underlying study. These HPV16-positive tonsillar squamous cell carcinomas furthermore showed the downregulation of cyclin D1, next to the accumulation of p14 ARF and p21 Cip1/WAF1 .…”

“…In contrast and as observed in our study, p53 is frequently upregulated in HPVnegative tumors due to mutations in the TP53 gene as a result of exposure to tobacco and/or alcohol. 10,16,20,27,47 Although p21 Cip1/WAF1 is known to be a downstream effector of p53, 48,49 it was surprising to find overexpression in HPV-positive tumors harboring low or no detectable levels of p53. Such observations have also been reported by Milde-Langosch et al 50 in HPV-associated uterine cervical tumors and suggest that also p53-independent mechanisms may lead to p21 Cip1/WAF1 accumulation as described previously.…”

“…9 It has been shown that there are several differences between HPV-positive and -negative headand-neck squamous cell carcinomas. Despite the fact that HPV positivity in head-and-neck squamous cell carcinomas is an indicator for favorable prognosis, from a clinical point of view these tumors are often poorly differentiated 4,6,[10][11][12] and metastasized to lymph nodes at presentation. 10,11 Furthermore, HPV-positive tumors are often smaller at first diagnosis (diameter r4 cm), 13 and associated with low/no exposure to alcohol and tobacco.…”

“…Despite the fact that HPV positivity in head-and-neck squamous cell carcinomas is an indicator for favorable prognosis, from a clinical point of view these tumors are often poorly differentiated 4,6,[10][11][12] and metastasized to lymph nodes at presentation. 10,11 Furthermore, HPV-positive tumors are often smaller at first diagnosis (diameter r4 cm), 13 and associated with low/no exposure to alcohol and tobacco. 10,11 At the molecular level, the functional inactivation of two key tumor suppressor proteins, ie, p53 and pRb by the HPV-derived oncoproteins E6 and E7, often result in the downregulation of p53, pRb, cyclin D1, and a strong upregulation of p16 INK4A in HPVpositive tumors.…”

“…10,11 Furthermore, HPV-positive tumors are often smaller at first diagnosis (diameter r4 cm), 13 and associated with low/no exposure to alcohol and tobacco. 10,11 At the molecular level, the functional inactivation of two key tumor suppressor proteins, ie, p53 and pRb by the HPV-derived oncoproteins E6 and E7, often result in the downregulation of p53, pRb, cyclin D1, and a strong upregulation of p16 INK4A in HPVpositive tumors. 5,7,[14][15][16] HPV-negative tumors, in contrast, often show inactivation of p16 INK4A , p53 overexpression as a result of gene mutations, cyclin D1 gene amplification and overexpression, as well as EGFR accumulation.…”