Integrin β4 Regulates Migratory Behavior of Keratinocytes by Determining Laminin-332 Organization

Abstract

Whether ␣6␤4 integrin regulates migration remains controversial. ␤4 integrin-deficient (JEB) keratinocytes display aberrant migration in that they move in circles, a behavior that mirrors the circular arrays of laminin (LM)-332 in their matrix. In contrast, wild-type keratinocytes and JEB keratinocytes, induced to express ␤4 integrin, assemble laminin-332 in linear tracks over which they migrate. Moreover, laminin-332-dependent migration of JEB keratinocytes along linear tracks is restored when cells are plated on wild-type keratinocyte matrix, whereas wild-type keratinocytes show rotation over circular arrays of laminn-332 in JEB keratinocyte matrix. The activities of Rac1 and the actin cytoskeleton-severing protein cofilin are low in JEB keratinocytes compared with wild-type cells but are rescued following expression of wild-type ␤4 integrin in JEB cells. Additionally, in wild-type keratinocytes Rac1 is complexed with ␣6␤4 integrin. Moreover, Rac1 or cofilin inactivation induces wild-type keratinocytes to move in circles over rings of laminin-332 in their matrix. Together these data indicate that laminin-332 matrix organization is determined by the ␣6␤4 integrin/actin cytoskeleton via Rac1/cofilin signaling. Furthermore, our results imply that the organizational state of laminin-332 is a key determinant of the motility behavior of keratinocytes, an essential element of skin wound healing and the successful invasion of epidermal-derived tumor cells.Migration of cells is an essential element of morphogenesis, remodeling following tissue damage and metastasis. For example, following wounding of the skin, epidermal cells migrate over a wound, a complex process involving changes in cytoskeleton organization, alterations in cell-cell and cell-matrix interactions, and modulation in gene and protein expression (1, 2).In particular, keratinocytes lose stable matrix adhesive structures called hemidesmosomes, migrate over exposed dermal collagen, and deposit a provisional matrix rich in laminin (LM) 3 -332 (old nomenclature: laminin-5), a heterotrimer consisting of ␣3, ␤3, and ␥2 subunits (1-5). This provisional matrix regulates the motility of keratinocytes (2-4). LM-332 is also believed to support tumor cell invasion (6 -12).Although cells in wounds and cancer cells migrate on a LM-332 substrate, LM-332 stabilizes epidermal cell adhesion in intact skin (3, 4,(12)(13)(14)(15)(16). These contradictory functions exhibited by LM-332, adhesion and motility, have been investigated by a number of laboratories, and results to date indicate that proteolytic processing of LM-332 has a profound impact on its functions. Specifically, in the extracellular matrix, the ␣3 and ␥2 subunits are processed from 190 to 160 kDa and from 140 to 100 kDa, respectively (4, 17-22). LM-332 containing an unprocessed ␣3 chain supports keratinocyte motility (20). Upon proteolytic cleavage of the ␣3 LM subunit within its G domain, LM-332 triggers hemidesmosome assembly, leading to decreased cell motility (3, 20 -24). However, further proteolysis of l...

Laminin-332-Integrin Interaction: A Target For Cancer Therapy?

“…Sehgal et al showed that β4 integrin-deficient (JEB) keratinocytes display aberrant migration; they move in circles, a behavior that mirrors the circular arrays of laminin-332 in their matrix [95]. In contrast, wild-type keratinocytes, and JEB keratinocytes induced to express β4 integrin, assemble laminin-332 in linear tracks over which they migrate.…”

Integrin Regulation of Epidermal Functions in Wounds

“…Although a 6 b 4 can regulate the motility of cultured keratinocytes, 72,73 it remains uncertain whether this integrin has important pro-migratory roles in wound re-epithelialization. It is clear that a 6 b 4 is not sufficient for normal wound reepithelialization in the absence of b 1 integrins, since b 1 -null epidermis shows severe migration defects.…”

“…73 a 3 b 1 . In vivo and in vitro studies have identified several roles for integrin a 3 b 1 in regulating keratinocyte functions that may contribute to wound healing, including ECM deposition and organization, 74,75 cell polarization and migration, 34,53 cell survival, 62 cell proliferation, 76 and secretion of ECM proteases and pro-angiogenic factors.…”

Targeting 14-3-3zeta in cancer therapy

“…Recent studies have suggested that the migration and invasion of tumor cells is controlled, in part, dependent on a6b4 integrin/ Rac1 signaling. 51,52 This pathway signals focus to the major regulator of cellular actin dynamics, cofilin, 53 its activity dependent on phosphorylation/dephosphorylation at Ser3, modulating cytoskeletal organization and cell migration. 14-3-3zeta protein involves in the regulation of cellular actin structures through the maintenance of phosphorylated-cofilin levels.…”