Olga M. Viquez

Integrin α3β1 regulates kidney collecting duct development via TRAF6-dependent K63-linked polyubiquitination of Akt

This study demonstrates that integrin α3β1 interactions with both α3- and α5-containing laminins regulate ureteric bud (UB) development by functionally modulating the Akt signaling pathway. In addition, the work done shows that K63-linked polyubiquitination plays a previously unrecognized role in integrin α3β1–dependent cell signaling required for UB development and that this may be a novel general mechanism whereby integrins regulate signaling pathways.

Screening 34 Peanut Introductions for Allergen Content Using ELISA

Peanut is one of the most allergenic foods and reports of accidental ingestion of peanuts in unsuspected food are increasing. No information is available on the allergen content of peanut germplasm grown commercially and used in the food and confectionery industry. The objectives of this study were: (1) to determine the allergen contents of 34 peanut introductions (PI); and (2) to identify naturally occurring allergen-free and/or low or hypoallergenic peanuts germplasm. A basic ELISA protocol was utilized to detect the presence of antigens in the peanut lines using a pool of human sera from patients with documented history of peanut allergy. Two naturally occurring low, or hypo-allergenic germplasm were identified as PI 261942 and PI 338386. Both are Valencia market types with total allergen content significantly lower (P ≤0.05) than that of PI 119880 (0.550), PI 119876 (0.415) and PI 118991 (0.410) three Valencia market types and PI 262111 (0.485), a Virginia market type. No allergen-free PI was found. Allergen content of peanut lines from Bolivia and Paraguay were significantly (P ≤0.05) different to those from Venezuela. No significant difference was observed in the allergen content of the four market types.

Integrin alpha6 maintains the structural integrity of the kidney collecting system

Laminins are a major constituent of the basement membranes of the kidney collecting system. Integrins, transmembrane receptors formed by non-covalently bound α and β subunits, serve as laminin receptors, but their role in development and homeostasis of the kidney collecting system is poorly defined. Integrin α3β1, one of the major laminin receptors, plays a minor role in kidney collecting system development, while the role of α6 containing integrins (α6β1 and α6β4), the other major laminin receptors, is unknown. Patients with mutations in α6 containing integrins not only develop epidermolysis bullosa, but also have abnormalities in the kidney collecting system. In this study, we show that selectively deleting the α6 or β4 integrin subunits at the initiation of ureteric bud development in mice does not affect morphogenesis. However, the collecting system becomes dilated and dysmorphic as the mice age. The collecting system in both null genotypes was also highly susceptible to unilateral ureteric obstruction injury with evidence of excessive tubule dilatation and epithelial cell apoptosis. Mechanistically, integrin α6-null collecting duct cells are unable to withstand high mechanical force when adhered to laminin. Thus, we conclude that α6 integrins are important for maintaining the integrity of the kidney collecting system by enhancing tight adhesion of the epithelial cells to the basement membrane. These data give a mechanistic explanation for the association between kidney collecting system abnormalities in patients and epidermolysis bullosa.

The laminin binding α3 and α6 integrins cooperate to promote epithelial cell adhesion and growth

Integrins, the major receptors for cell-extracellular matrix (ECM) interactions, regulate multiple cell biological processes including adhesion, migration, proliferation and growth factor-dependent signaling. The principal laminin (LM) binding integrins α3β1, α6β1 and α6β4 are usually co-expressed in cells and bind to multiple laminins with different affinities making it difficult to define their specific function. In this study, we generated kidney epithelial collecting duct (CD) cells that lack both the α3 and α6 integrin subunits. This deletion impaired cell adhesion and migration to LM-332 and LM-511 more than deleting α3 or α6 alone. Cell adhesion mediated by both α3β1 and α6 integrins was PI3K independent, but required K63-linked polyubiquitination of Akt by the ubiquitin-modifying enzyme TRAF6. Moreover, we provide evidence that glial-derived neurotrophic factor (GDNF) and fibroblast growth factor 10 (FGF10)- mediated cell signaling, spreading and proliferation were severely compromised in double integrin α3/α6- but not single α3- or α6-null CD cells. Interestingly, these growth factor-dependent cell functions required both PI3K- and TRAF6-dependent Akt activation. These data suggest that expression of the integrin α3 or α6 subunit is sufficient to mediate GDNF- and FGF10-dependent spreading, proliferation and signaling on LM-511. Thus, our study shows that α3 and α6 containing integrins promote distinct functions and signaling by CD cells on laminin substrata.