br Discussion Genetic variants in receptors
Discussion Genetic variants in receptors for viral entry and/or oncogenesis have been documented to have functional consequences for pathogenicity. The genetic factors underlying susceptibility to KSHV infection and KS development are not fully understood. We therefore set out to identify sequence variants in EPHA2, being both an entry ABT-263 (Navitoclax) for KSHV [22,23] as well as being upregulated in various tumours, including KS [22,, , , ], in South African HIV-infected patients, and to determine the association of any identified EPHA2 variants with susceptibility to KSHV infection and/or KS development. As AIDS-related KS is by far the most common form of the KSHV-associated malignancies and particularly affects individuals in Sub-Saharan Africa due to the HIV/AIDS epidemic , we restricted the recruitment of patients to HIV-infected individuals from this geographical region, presenting at hospitals in the Western Cape province of South Africa. In support with the reported disproportionately high KSHV seroprevalence in sub-Saharan Africa (>50%) compared to world prevalence rates (<10%), which has not significantly changed since the onset of the HIV/AIDS epidemic , we determined a 31.6% (95% CI 28.3–35.1%) KSHV seropositivity in our total KS− patient cohort (Table 2), presenting the first assessment of KSHV seroprevalence in the Western Cape Province of South Africa. This is in agreement with earlier studies conducted in Soweto, Johannesburg and Kwa-Zulu Natal, which have indicated that KSHV seroprevalence is between 30–40% . Despite the high HIV/KSHV seroprevalence in sub-Saharan Africa, not all co-infected patients develop KS. To elucidate a potential underlying genetic predisposition due to variants in the EPHA2 protein, we performed aggregate variation across the entire EPHA2 coding region to assess a retrospective candidate gene association with KSHV infectivity and/or KS prevalence. Since mother-to-child transmission via saliva is thought to be the primary route of KSHV transmission , the extent of later sexual transmission that could be confounding for KSHV infection is thought to be minimal [45,46]. All patients recruited to this study were adults between 19 and 72 years of age (Interquartile Range: 31–47, see Table 1); therefore, it can be assumed that their exposure to and infection with KSHV has been concluded at the time of recruitment. We identified missense variants and variants within the functionally important Pkinase-Tyr and SAM domains, specifically 2254 T > C (located in the Pkinase-Tyr domain) and 2990 G > T (located in the SAM domain) which were associated with KS, Table 3. Each of these variants was designated a ‘probably damaging’ annotation when assessed for functional impact using the PolyPhen-2 prediction tool. Interestingly, additional individual Pkinase-Tyr domain variants spanning exons 12–15 (particularly 2688 G > C (rs765280326), 2727 C > T, 2325 G > C (rs747058254) and 2047 T > C (rs34021505)), although not significantly associated with KS, were found to be overrepresented among KS patients (group 1), Table 3 and Fig. 1. We can speculate that, although rare, their functional impact may be important, represented by the significant association of aggregate Pkinase-Tyr variation with KS. It is plausible that they may enhance EPHA2 Pkinase-Tyr signalling which is essential for the function of the EPHA2 receptor and which has been linked to a metastatic, aggressive phenotype in a number of cancers [, , , ]. The variant 2990 G > T (located in the cytoplasmic SAM protein interaction domain), found to be overrepresented among patients with KS (Table 3) may further contribute to oncogenesis by altering the function of the SAM, a protein-protein interaction region suggested to bind adaptor proteins thereby mediating the downstream signalling events triggered by EPHA2 activation [47,48].