Abstract 4268: Resistance to growth inhibition by transforming growth factor-beta is associated with activation of the PI3K-Akt pathway in HPV16-immortalized human keratinocytes at late stages of in vitro progression.

Transforming growth factor-beta (TGF-s) plays a vital role in embryonic development, cell proliferation, inflammation and wound repair. The Smad proteins are the central mediators of TGF-s signal transduction. However, recently several non-Smad pathways (ex., Erk, Jnk, p38 MAPK, PI3K-Akt) have been determined to play key roles in TGF-s signaling. TGF-s signaling is often disrupted in cancer, including cervical cancer. Human papillomavirus (HPV) is the main etiological agent in cervical cancer. HPV type 16 (HPV16)-immortalized human keratinocytes (HKc/HPV16) are initially very sensitive to growth inhibition by TGF-s. However, HKc/HPV16 become increasingly resistant to TGF-s during in vitro progression, and are completely resistant to TGF-s-induced growth inhibition at late-stages of transformation, when they exhibit a differentiation resistant phenotype (HKc/DR). Although HKc/DR are completely resistant to the growth inhibitory effects of TGF-s, some Smad signaling remains. A reporter construct containing tandem repeats of Smad binding elements was induced by TGF-s in HKc/DR at about 50% of the level observed in HKc/HPV16. Furthermore, TGF-s was capable of inducing epithelial-mesenchymal transition (EMT) in HKc/DR. To further explore TGF-s signaling in HKc/HPV16 and HKc/DR, we used phospho specific antibody microarrays from Full Moon BioSystems. These arrays feature phospho and non-phospho pairs of specific antibodies pertinent to the TGF-s pathway. Protein extracts from HKc/HPV16 and HKc/DR untreated or treated for 90 min with 40 pM TGF-s were compared on the antibody microarrays. Activation of the Akt pathway by TGF-s was observed in HKc/DR but not in HKc/HPV16. Similarly, PI3K and mTOR showed activation by TGF-s in HKc/DR but not HKc/HPV16. We conclude that TGF-s signals primarily through Smad-dependent pathways to inhibit cell proliferation in HKc/HPV16, but that non-canonical (non-smad) signaling through the PI3K-Akt-mTOR axis predominates in HKc/DR. Citation Format: Rupa Velidandla, Gehana Vaswani, Sangeeta Kowli, Lucia Pirisi-Creek, Kim E. Creek. Resistance to growth inhibition by transforming growth factor-beta is associated with activation of the PI3K-Akt pathway in HPV16-immortalized human keratinocytes at late stages of in vitro progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4268. doi:10.1158/1538-7445.AM2013-4268