Requirement of Rac1 distinguishes follicular from interfollicular epithelial stem cells

Epithelial stem cells in the bulge region within the hair follicle maintain the cyclic hair growth, but whether these stem cells also contribute to the epidermal renewal remains unclear. Here, we observed that the conditional deletion of the Rac1 gene in the mouse skin, including the potential follicular and epidermal stem cell compartments, results in alopecia owing to defective hair development. Surprisingly, mice lacking the expression of this Rho GTPase do not display major alterations in the interfollicular skin. Furthermore, Rac1 excision from primary epithelial keratinocytes results in the inability to reconstitute hair follicles and sebaceous glands when grafted onto mice, but epithelial cells lacking Rac1 can nonetheless form a healthy epidermis. Together, these findings support the emerging view that the epidermis and the hair follicles are maintained by different epithelial stem cells, and provide evidence that the requirement for Rac1 function can distinguish these distinct stem cells populations.

Molecular cross-talk between the NFkappaB and STAT3 signaling pathways in head and neck squamous cell carcinoma

The development of head and neck squamous cell carcinoma (HNSCC) involves the accumulation of genetic and epigenetic alterations in tumor-suppressor proteins, together with the persistent activation of growth-promoting signaling pathways. The activation of epidermal growth factor receptor (EGFR) is a frequent event in HNSCC. However, EGFR-independent mechanisms also contribute to the activation of key intracellular signaling routes, including signal transducer and activator of transcription-3 (STAT3), nuclear factor kappaB (NFkappaB), and Akt. Indeed, the autocrine activation of the gp130 cytokine receptor in HNSCC cells by tumor-released cytokines, such as IL-6, can result in the EGFR-independent activation of STAT3. In this study, we explored the nature of the molecular mechanism underlying enhanced IL-6 secretion in HNSCC cells. We found that HNSCC cells display an increased activity of the IL-6 promoter, which is dependent on the presence of an intact NFkappaB site. Furthermore, NFkappaB inhibition downregulated IL-6 gene and protein expression, and decreased the release of multiple cytokines. Interestingly, interfering with NFkappaB function also prevented the autocrine/paracrine activation of STAT3 in HNSCC cells. These findings demonstrate a cross-talk between the NFkappaB and the STAT3 signaling systems, and support the emerging notion that HNSCC results from the aberrant activity of a signaling network.

Osteolipoma: a rare lesion in the oral cavity

We present the case of a 65-year-old woman who had a painless mass in the left buccal mucosa. Histology showed a benign osteolipoma.