Environmental stimuli responsible for inducing cutaneous inflammation include contact allergens and ultraviolet light. We postulate that these diverse stimuli trigger a cutaneous inflammatory response by directly inducing epidermal keratinocytes to elaborate specific pro-inflammatory cytokines and adhesion molecules. The consequences are activation of dermal microvascular endothelial cells and selective accumulation of specific mononuclear cells in the dermis and epidermis. Thus, keratinocytes may act as "signal transducers", capable of converting exogenous stimuli into the production of cytokines, adhesion molecules, and chemotactic factors (acting in an autocrine and paracrine fashion) responsible for initiation of "antigen-independent" cutaneous inflammation. The initiation phase may facilitate or promote an amplification phase with additional production of tumour-necrosis factor alpha and interferon gamma via an "antigen-dependent" pathway, and keratinocyte/T cell/antigen-presenting dendritic cellular associations. The direct activation of keratinocytes, with their ability to produce the complete repertoire of pro-inflammatory cytokines, can profoundly influence endogenous and recruited immunocompetent cells, thereby providing the critical trigger responsible for the swift and clinically dramatic alterations that occur following contact between the epidermis and a host of "noxious" agents.

T lymphocytes and mononuclear cells preferentially accumulate in the epidermis in inflammatory skin disease. To determine the role of keratinocytes in both the chemotaxis and adhesion of these cells to the epidermis, cultured keratinocytes were incubated with IFN-y and tumor necrosis factor-alpha (TNF-a), and mRNA detected and quantitated for IL-8, monocyte chemotaxis and activating factor, and intercellular adhesion molecule-I. Whereas induction of these mRNAs was either absent, or relatively weak and transient, to either IFN-y or TNF-a alone, when administered in combination there was a dramatic increase and persistence in the induction of all three genes. Pretreatment of the keratinocytes with cycloheximide failed to eliminate transcription, implying that all three are primary response genes. Transforming growth factor-beta, which modulates other keratinocyte functions (not related to adhesion or chemotaxis of inflammatory cells) failed to induce any of the genes. These novel findings potentially explain the selective recruitment of T cells and monocytes observed in inflammatory skin disease, because IFN-'y and TNF-a can coordinately regulate keratinocyte-derived chemoattractants and adhesion molecule production. (J. Clin. Invest. 1990.85:605-608.) epidermis -lymphocytes -macrophages -psoriasis -trafficking

The objective of the current study was to investigate the effects of Rap1GAP on invasion and progression of head and neck squamous cell carcinoma (SCC) and the role of matrix metalloproteinase (MMP) 9 and MMP2 in this process. Rap1GAP functions by switching off Rap1, the Ras-like protein that has been associated with carcinogenesis. Previous findings suggest that Rap1GAP acts as a tumor suppressor protein in SCC by delaying the G 1 -S transition of the cell cycle. However, cells transfected with Rap1GAP exhibit a more invasive phenotype than corresponding vector-transfected control cells. MMP2 and MMP9 are enzymes that mediate SCC invasion via degradation of the extracellular matrix. Using SCC cells transfected with empty vector or Rap1GAP, cell invasion and MMP secretion were determined by Matrigel assays and gelatin zymography, respectively. Rap1GAP upregulated transcription and secretion of MMP2 and MMP9, as assayed by quantitative reverse transcription-PCR and zymography. Furthermore, chemical and RNA interference blockade of MMP2/MMP9 inhibited invasion by Rap1GAP-transfected cells. Immunohistochemical staining of a human oropharyngeal SCC tissue microarray showed that Rap1GAP and MMP9 expression and staining intensity are correlated (P < 0.0001) and that, in early N-stage lesions of SCC, high MMP9 is prognostic of poor disease-specific survival (P < 0.05). Furthermore, Rap1GAP staining is correlated with MMP2 (P < 0.03). MMP2 in combination with N stage has a prognostic effect on time to indication of surgery at primary site. MMP2 intensity is also positively correlated with T stage (P < 0.015). In conclusion, Rap1GAP inhibits tumor growth but induces MMP2-and MMP9-mediated SCC invasion and tumor progression, suggesting a role for this protein as a biomarker for early N-stage, aggressive SCCs. [Cancer Res 2008;68(10):3959-69]

Rap1, a growth regulatory protein that is strongly expressed in human squamous cell carcinoma (SCC), is inactivated by rap1GAP. Recent evidence in normal rat cells suggests that rap1GAP regulates proliferation. The objective of the current study was to investigate whether rap1GAP functions as a tumor suppressor in SCC. Using a pull-down assay, active GTP-bound rap1 was up-regulated in SCC compared to normal or immortalized keratinocytes. Because both rap1A and rap1B isoforms of rap1 are expressed in SCC, the rap1GAP inactivation of both rap1 isoforms was verified using cells transfected with EGFP-rap1A or EGFP-rap1B or co-transfected with FLAG-tagged rap1GAP. The results demonstrate that expression of rap1GAP in oropharyngeal SCC down-regulated active rap1, ERK activation, and proliferation. Rap1A and rap1B are ras-like proteins that are ubiquitously expressed. Rap1A, which is also referred to as smg p21 or Krev1, shares 95% homology with rap1B, differing by only nine amino acids (of a total of 184), six of which are located at the C-terminus between amino acids 171 to 184.1 Active rap1 modulates cellular functions by regulating the translocation of other proteins or by shuttling between intracellular compartments.

Signaling through the epidermal growth factor receptor (EGFR) has been primarily implicated in the growth of epithelial cells including keratinocytes. However, the mechanism by which EGFR stimulation promotes keratinocyte cell growth is poorly understood. Here we report that human keratinocytes undergo apoptosis when incubated with the blocking EGFR monoclonal antibody 225 IgG, or PD153035, a highly speci®c EGFR tyrosine kinase inhibitor. Endogenous mRNA and protein levels of Bcl-X L , a member the Bcl-2 family which suppresses apoptosis, were speci®cally inhibited by EGFR blockade. Furthermore, stimulation of EGFR signaling through two natural ligands, transforming growth factor (TGF)-a and epidermal growth factor (EGF), increased the expression of Bcl-X L in quiescent keratinocytes and HaCaT cells. Finally, ectopic expression of Bcl-X L in HaCaT cells increased survival after EGFR blockade when compared to untransfected cells or HaCaT keratinocytes transfected with empty vector. These results suggest that the anti-apoptotic protein Bcl-X L plays an important role in the maintenance of keratinocyte survival in response to EGFR signaling.