Figure 2. Integrins crosstalk with growth factor receptors to regulate proliferation in the basal layer.

The stratum basale has a high density of hemidesmosomes and integrin-based adhesions that maintain cell attachment to the underlying basement membrane, which is composed of the lamina lucida and lamina densa. Hemidesmosomes connect to the basement membrane through α6β4 integrins and the transmembrane protein bullous pemphigoid antigen 2 (BPAG2; also known as collagen XVII), and are tethered to intermediate filaments by the plakin family members plectin and BPAG1e⁶. α3β1 integrins provide transmembrane connections to the intracellular actin network through recruitment of several factors to their cytoplasmic tails. Integrins are thought to crosstalk with receptors such as EGFR (epidermal growth factor receptor) to induce proliferation of cells in the stratum basale via mitogen-activated protein kinase (MAPK) signalling. As cells stratify, decreased integrin density allows cell cycle exit and differentiation.