In general, eukaryoticcell of human contains genes composed of a double-strandedcoiled molecule known as deoxyribonucleic acid (DNA). The nucleotides sequences of DNA produce different types ofprotein which act as effectors molecule as well as participated in manydifferent types cellular functions. In normal conditions,various tightly controlled excitatory and inhibitory pathways regulate to oralepithelial cell biology such as cell division, differentiation, and program celldeath (apoptosis). An extracellularligand like growth factor (a protein) bindswith a specific cell surface receptor. The receptor-ligand complex generates excitatory or inhibitory signals sentthrough intracellular and nuclear messengers that can either alter cellfunction by changing the effect of proteins.
Carcinogenesisis a complex, multistep process in which genetic events within signaltransduction pathways are altered resulting enhance to cell viability forproliferation, uncontrolled apoptosis, or grow by invading locally ormetastasizing to distant sites. The histologicalprogression of oral carcinogenesis is believed to reflect the accumulation ofthese changes (Basu &Krishnamurthy, 2010).The development ofsquamous cell carcinoma of the oral cavity is considered a complex multistepprocess. It has been reported that normal oral mucosalkeratinocytes are chronically exposed to risk factors, which can break thehomeostasis and generate genetic instability. There arevarious genetic alterations in the development of this stage occurring in p53, CyclinD1, EGFR (epidermal growth factor receptor),NOTCH1 (Notch homolog 1), CDKN2A (cyclin-dependent kinase inhibitor 2a), STAT3 (signaltransducer and activator of transcription 3), and Rb (retinoblastoma).
The proliferationand uncontrolled growth gain adaptive advantages over the surrounding cells,which promote local invasion and collaboration of the surrounding epithelialcells. Moreover, there are many factors secreted from cancercells to contribute the development of cancer cell progression including MMP2 (matrix metalloproteinase 2), MMP9 (matrix metalloproteinase 9), MMP13 (matrix metalloproteinase 13), ROS (reactive oxygen species), VEGF (vascular endothelial growth factor), CXCL1chemokine (CXC motif) ligand1, CXCL8 chemokine (CXCmotif) ligand 8, PDGF (platelet-derived growth factor), IL-8(inteleukin 8), FGF-2(fibroblast growth factor 2), TGF-? (transforming growth factor-?), TNF-? (tumor necrosis factor-?),IL-1 (inteleukin 1),GMCSF (granulocye-macrophage colony-stimulating factor). This microenvironmentpromotes cell adhesion loss (such as E-cadherin) and facilitates epitheliummesenchymal transition (EMT),Vimentin, and N-cadherin can be expressed in these cells. CAFs (tumor-associatedfibroblasts) are used as a specific tumor marker including?-SMA (?-smoothmuscle actin) and integrin ?6. Endothelinscan contribute to pro-migratory paracrine signalingbetween CAFs and oral cancer cells. It also promotes CXCL1and CXCL8 endothelial cell proliferation and survival. Endothelialcells produce factors like EGF, which increase migrationof cancer cells (Rivera, Christiansen, & Sullivan,2015).