Oral Carcinogenesis

Dental & Craniofacial Research

Investigators

Linked publications & trials

Abstract

Genomic and proteomic approaches to understand oral cancer [unreadable] [unreadable] Although risk factors for HNSCC, such as alcohol and tobacco consumption, are well recognized, the molecular mechanisms responsible for this malignancy are still not fully understood. We have used a number of novel approaches to investigate gene and protein expression profiles in HNSCC. We have shown that laser capture microdissection (LCM) can be used to procure specific cell populations from heterogenous tumor samples, and that LCM-procured material can be used effectively to extract RNA, DNA, and proteins. We have teamed up with other research institutions to conduct gene and protein expression analysis of HNSCC by combining LCM, gene arrays, and proteomic platforms. These efforts have already provided a wealth of information about the distinctive pattern of gene and protein expression in HNSCC. [unreadable] [unreadable] Proteome-wide analysis of HNSCC tissues using LCM and mass spectrometry. Ultimately, the aberrant expression and activity of molecules present in HNSCC cells are responsible for their malignant behavior. Thus, we have recently made a concerted effort to investigate protein expression profiles during HNSCC tumor development. While in prior studies we have investigated protein expression profiles in frozen HNSCC samples, we now explored the use of standard formalin-fixed paraffin-embedded (FFPE) tissues for proteomic analysis, as they preserve the tissue architecture and may reflect better the protein composition as it exists in vivo. We combined LCM with protein extraction procedures and highly sensitive mass spectrometry techniques to identify proteins expressed in normal oral squamous epithelium and HNSCCs displaying distinct differentiation patterns. Mass spectrometry and bioinformatic analysis led to the identification of large numbers of molecules, including cytokeratins, differentiation markers, and proteins involved in stem cell maintenance, signal transduction, migration, cell cycle regulation, angiogenesis, matrix degradation, and proteins with tumor suppressive and oncogenic potential. Representative proteins were further validated using immunohistochemical studies in HNSCC tissue sections and tissue microarrays. Taken together, the ability to combine LCM and in-depth proteomic analysis of FFPE tissues provided valuable information regarding the nature of the proteins expressed in normal squamous epithelium and during HNSCC progression. [unreadable] [unreadable] [unreadable] Dysregulated signaling networks in HNSCC: novel mechanism-based approaches for HSNCC treatment [unreadable] [unreadable] There is an urgent need for new treatment options for HNSCC patients, considering that their overall 5-year survival is relatively low (50%) and has not improved much over the past 3 decades. The emerging information on the nature of the deregulated molecular mechanisms responsible for HNSCC progression has provided the possibility of exploring new mechanisms-based therapeutic approaches for HNSCC. For example, we have observed that persistent activation of the serine-threonine kinase Akt is a frequent event in HNSCC, and that its blockade inhibits tumor cell growth. Among the many molecules whose activity is regulated by Akt, we have made a focal effort on the mammalian target of rapamycin (mTOR), an atypical kinase that seats at the cross-road between energy sensing and growth promoting signaling pathways. We have shown that a high fraction of HNSCC clinical samples exhibit high levels of phosphorylated ribosomal S6 protein (pS6), the most downstream target of the Akt-mTOR pathway, and that inhibition of mTOR by the use of rapamycin causes the rapid decrease in the level of pS6 and the apoptotic death of HNSCC tumor xenografts, thereby causing tumor regression. These efforts have identified the Akt-mTOR pathway as a potential therapeutic target for HNSCC.[unreadable] [unreadable] The Head and Neck Tissue Array Initiative: Dissection of the Akt-mTOR signaling network. As an approach to evaluate the expression pattern and status of activation of signaling pathways in clinical specimens from HNSCC patients, we established the Head and Neck Cancer Tissue Array Initiative, an international consortium aimed at developing a high density oral specific HNSCC tissue microarray. Emerging information by the use of phospho-specific antibodies detecting the activated state of signaling molecules indicates that the Akt/mTOR pathway is frequently activated in HNSCC, but independently from the activation of EGFR or the detection of mutant p53. Indeed, we identified a large group of tissue samples displaying active Akt and mTOR in the absence of EGFR activation. Furthermore, we have also identified a small subgroup of patients in which the mTOR pathway is activated but not Akt, suggesting the existence of an Akt-independent signaling route stimulating mTOR. These findings provide important information about the nature of the dysregulated signaling networks in HNSCC, and may also provide the rationale for the future selection of HNSCC patients that may benefit from novel mechanism-based therapies.[unreadable] [unreadable] Animal models for oral malignancies [unreadable] [unreadable] A major limitation in the area of HNSCC research is the limited availability of animal models to test the validity of current genetic paradigms of tumorigenesis, and to explore the effectiveness of treatment modalities or chemopreventive approaches. We have been using our recently developed tetracycline-inducible system to express oncogenes in the skin and oral mucosa and other conditional animal systems to explore the contribution of recently identified dysregulated molecular mechanism to SCC progression. [unreadable] [unreadable] Requirement of Rac1 distinguishes follicular from interfollicular epithelial stem cells. Many cancers appear to arise from the accumulation of genetic alterations in resident, tissue-specific stem cells, or in cells that have regained stem-cell like features. This prompted us to initiate an effort to identify potential oral epithelial stem cells. It is still unclear whether oral and interfollicular epithelial stem cells are distinct from the better characterized hair-follicle stem cells. As follicular stem cells need to migrate from the bulge region of the hair to the bulb to start a new hair cycle, we hypothesized that disrupting molecules involved in epithelial cell migration may help distinguish these two stem cell populations. In this regard, the small GTPase Rac1 plays a central role in cell motility. Thus, in a recent study we conditionally deleted Rac1 from squamous epithelium. Surprisingly, we observed that although mice lacking Rac1 expression in the skin and oral mucosa exhibit alopecia due to the defective hair development, they do not display any major alterations in their interfollicular skin and oral epithelium. Furthermore, Rac1 excision from newborn mice epithelial cells results in the inability of their residing stem cells to reconstitute hair follicles, but they can nonetheless regenerate a healthy epidermis. Together, these findings supported the emerging view that the oral mucosa and epidermis are maintained by different stem cell compartments than those regenerating the hair follicles, and that these distinct stem cell populations can be distinguished molecularly by their requirement for Rac1 function.