It is widely accepted that EBV is etiologically associated with NPC; but it is proven that other co-factors might be involved in the carcinogenesis process. HPVs are considered to be one of those factors since they possess the ability to transform epithelial cells and a significant number of NPC biopsies harbour HPV DNA [12
]. We report here that 34% (24/70) from Moroccan NPC biopsies harbour HPVs. These results are in agreement with other studies reporting the same prevalence of HPV DNA in NPC cases. In fact, using the same consensus primers, HPV DNA was detected in 31 of 103 NPC samples (30%) [8
]. Moreover, Krishna et al.
have shown that HPV DNA was detected in 38.8% of 36 southern Indian NPC cases [14
]. Tung et al.
in Eighty-eight fresh tissue samples of NPC showed that HPV DNA was detected in 51% of the specimens [15
Coinfection by HPV and EBV has not been well documented and the significance of the presence of both viruses in nasopharyngeal cells has not been determined. In our study, coinfection with both viruses was observed in 34% of patients. Tung et al.
showed that among 88 fresh NPC specimens from Chinese population, coexistence of EBV and HPV DNA was observed in 42% of samples [15
Of interest, EBV was detected also in CC specimens from Indonesian patients, and 68% of analysed cases are co-infected with HPV and EBV [16
]. In our study, HPV and EBV co-infection seems to be less frequent in NPC. Theses differences may be due to the population' characteristics and the dissemination power of HPV in the population.
Our results show no correlation between HPV status with either age or gender in NPC patients. These findings are supported by other studies that reported no significant differences [17
]. However, Zhang et al. showed that HPV infection either in oral squamous cell carcinoma or normal mucosa was observed with a higher frequency in men (81.3%) compared with that in women (60%) [19
]. to evaluate the association between HPV status and, age and/or gender, in NPC cases, a study with a large sampling is needed.
With regard to HPV genotypes, HPV31 was the most frequent genotype in Moroccan NPC patients (20.8%). The same genotype was also frequently found in tonsils and nasopharyngeal cells in western Mexico NPC cases [20
]. The second prevalent HPV type detected in our NPC biopsies is HPV59 (16,7%). Of interest, HPV-16 and -18, which are the most virulent genotypes associated with CC in Moroccan woman (35% to 45%) [21
], were detected in very few Moroccan NPC cases (8.3%), and similar data were reported in an Iranian study [23
Geographic and racial distinctions have been identified between NPC of the Far East versus those diagnosed in Caucasian American patients with regard to the interrelationship of histologic subtype and HPV infection. In fact, HPV are detected more often (50%) in type I NPC from American Caucasian patients than type III [6
]. In our study, one of two WHO-I and 22 of 68 WHO-II/III NPCs tumors were HPV positive. The very low number of NPC type-I cases available for comparison, reflecting the rarity of WHO-I tumors in NPC patients from Morocco, did not allow us to evaluate the relationship between HPV and NPC histologic subtype.
Taken together, these data suggest that i) HPV genotypes associated with NPC are different from those consistently found in CC and ii) the HPV genotypes associated with NPC are not geo-specific.
HPV and EBV co-infections have not been well documented and the significance of the presence of both viruses in nasopharyngeal cells has not been determined. It has been shown that ZEBRA, an EBV immediate early protein expressed during lytic replication that activates early EBV genes, binds to p53 [24
]. The physical interaction of the ZEBRA and p53 protein prevents p53 from activating p53-responsive promoters [25
]. Similarly, HPV has been found to interact with p53, suggesting that this interaction promotes cell growth and thereby enhance viral replication [27
]. Targeting p53 may be a common requirement for the replication of many types of DNA viruses [16
]. In addition, B cells transfected with EBV latent membrane protein lost the regulatory effects of the retinoblastoma (RB) protein, and the HPV E7 transcript has been shown to immunoprecipitate the RB protein [28
]. Thus, the functional loss of the RB protein might be one event common to both the HPV and EBV carcinogenic pathways. Further investigations to evaluate the expression of viral genes, especially the E6 and E7 oncogenes, are necessary to identify the possible role of HPV infection in NPC development. These investigations could lead to the development of screening programs, new therapeutic approaches and specific methods of prevention, especially in high incidence areas.
On the other hand, further studies to evaluate the impact of EBV and HPV coinfection in cervical and nasopharyngeal carcinogenesis and molecular mechanisms implicated in tumor development are warranted.