Receptor Tyrosine Kinases EGFR Research Articles

EGF receptor attenuates Dpp signaling and helps to distinguish the wing and leg cell fates in Drosophila.

Wing and leg precursors of Drosophila are recruited from a common pool of ectodermal cells expressing the homeobox gene Dll. Induction by Dpp promotes this cell fate decision toward the wing and proximal leg. We report here that the receptor tyrosine kinase EGFR antagonizes the wing-promoting function of Dpp and allows recruitment of leg precursor cells from uncommitted ectodermal cells. By monitoring the spatial distribution of cells responding to Dpp and EGFR, we show that nuclear transduction of the two signals peaks at different position along the dorsoventral axis when the fates of wing and leg discs are specified and that the balance of the two signals assessed within the nucleus determines the number of cells recruited to the wing. Differential activation of the two signals and the cross talk between them critically affect this cell fate choice.

Activation of EGF receptor family members suppresses the cytotoxic effects of tumor necrosis factor-alpha.

Tumor necrosis factor (TNF)-alpha has a broad range of biological activities, which depend heavily on cell type and physiological condition. In a panel of human tumor cell lines we analyzed expression of the receptor tyrosine kinases EGFR, ErbB2 and ErbB3, and the response to TNF-alpha. Among the cell lines tested those resistant to TNF-alpha were found to express high levels of either EGFR, or ErbB2 and ErbB3. In TNF-sensitive breast and cervical carcinoma cells activation of EGFR or ErbB2 by the exogenous growth factors EGF and heregulin beta1 resulted in a significant increase in the number of cells surviving TNF-alpha treatment. In contrast, inhibition of EGFR activation in TNF-resistant breast carcinoma cells by the novel antagonistic anti-EGFR antibody 14E1 sensitized the cells to the cytotoxic effects of TNF-alpha. A bacterially expressed fusion protein consisting of a 14E1 single-chain (sc) Fv antibody fragment linked to human TNF-alpha retained TNF-alpha activity. This scFv(14E1)-TNF-alpha molecule localized specifically to EGFR on the surface of tumor cells and activated the NF-kappaB pathway in co-cultured T cells, as demonstrated by electrophoretic mobility shift assays.

Differential effects of aroclors and DDT on growth factor gene expression and receptor tyrosine kinase activity in human breast epithelial cells.

Breast cancer is a proliferative disease of mammary cells. Growth factors and growth factor receptors have been shown to play significant roles in breast cancer development and progression. Overexpression of growth factor receptors is commonly detected in primary breast cancers and predicts for a poor clinical prognosis. Environmental polychlorinated hydrocarbons have also been suggested as playing a role in breast cancer development, since polychlorinated biphenyls and DDT have been detected in the breast fat of women with malignant tumors and some of these agents possess estrogenic properties. We have examined the effects of these chemicals on growth factor receptor expression and receptor tyrosine kinase activity in the MCFlOAneoT human breast epithelial cell lines. The results of this research show that aroclor 1221 and 1254, while failing to affect the expression of c-erbB2 or c-Met growth factor receptors, stimulated the receptor tyrosine kinase activity of these receptors. Aroclor 1221 at 0.01 μM and aroclor 1254 at 0.1 μM stimulated c-Met tyrosine phosphorylation by ~7- and 3-fold, respectively, at 24 h post-treatment. p, pβ-DDT, a strongly estrogenic chemical stimulated EGFR receptor tyrosine kinase activity by ~4- and 5-fold at 0.01 and 0.1 μM, respectively. The results obtained from these studies show that these chemicals are capable of stimulating growth factor receptor tyrosine kinase activity and continuing research will provide valuable information on the effects of these chemicals on growth factor receptor-mediated signal transduction processes and the mechanism(s) by which these chemicals may affect cell proliferation and differentiation.

BrainiacEncodes a Novel, Putative Secreted Protein That Cooperates with Grk TGFα in the Genesis of the Follicular Epithelium

brainiac (brn)is involved in a number of developmental events. In addition to being required zygotically for segregation of neuroblasts from epidermoblasts, it is essential for a series of critical steps during oogenesis which also depend upongurken (grk),a TGFα homolog. Animals harboring strong mutations of eithergrkor EGF receptor tyrosine kinase (Egfr) or doubly mutant forbrnand weakgrkorEgfrmutations produce ovarian follicles with multiple sets of nurse cell–oocyte complexes. These follicles frequently have discontinuities in the follicular epithelium that uncover nurse cells but not the oocyte. Gaps first appear in the germarium, suggesting that some nurse cells lack affinity for invading prefollicular cells. This is the first evidence thatgrk,in addition to its involvement in the genesis of anterior–posterior and dorsal–ventral polarity, is also required for Egfr-dependent development of the follicular epithelium that surrounds each nurse cell/oocyte cluster to form an egg chamber. We have used restriction fragment length polymorphisms to localizebrnto a 10-kb region within a 300-kb stretch of DNA on the X-chromosome, and we have identified thebrngene by means of RNA rescue.brncodes for a putative secreted protein.brnis expressed in germ cells at the time follicle cells first surround the nurse cell–oocyte complex. Our genetic data suggest thatbrnacts in a parallel, but partially overlapping pathway to the Grk–Egfr signaling pathway. Thebrnpathway may help to provide specificity to TGFα–Egfr function during oogenesis.

Ultraviolet B injury increases prostaglandin synthesis through a tyrosine kinase-dependent pathway. Evidence for UVB-induced epidermal growth factor receptor activation.

To study the signal transduction mechanisms by which ultraviolet B (UVB) leads to increased prostaglandin E2 (PGE2) synthesis, human epidermal cultures were irradiated with 30 mJ/cm2 UVB and assayed for 6-h cumulative PGE2. Supernatants from irradiated cultures showed a 4-fold increase in PGE2 synthesis (113.6 +/- 26.8 pg/mg protein) when compared to supernatants from sham-irradiated cultures (25.6 +/- 3.9 pg/mg protein). Pretreatment of irradiated cultures with genistein (10 micrograms/ml) or tyrphostin-23 (50 microM), inhibitors of tyrosine kinases, blocked UVB-stimulated PGE2 synthesis. Treatment of nonirradiated cultures with epidermal growth factor (EGF), which acts through the receptor tyrosine kinase EGF-R, produced a 4-fold increase in PGE2 synthesis. However, addition of EGF to irradiated cultures did not further enhance their PGE2 synthesis, indicating irradiation rendered them refractory to EGF stimulation. In contrast, irradiated cultures could still significantly increase their PGE2 synthesis in response to the calcium ionophore A23187 or the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate, suggesting that the lack of response to EGF was selective. Furthermore, anti-phosphotyrosine immunoblot analysis revealed UVB-induced phosphorylation of tyrosine residues of EGF-R, an indicator of receptor activation. Phosphorylation was maximal 30-60 min after irradiation and was blocked by the tyrosine kinase inhibitors, genistein and tyrphostin. The antioxidant N-acetylcysteine decreased UVB-induced EGF-R tyrosine phosphorylation and PGE2 synthesis to near-basal levels. Conversely, treatment of unirradiated cultures with the potent oxidant tert-butyl-hydroperoxide (100 microM) increased both PGE2 synthesis and EGF-R phosphorylation. Collectively, these data suggest that antioxidant depletion induced by UV results in tyrosine phosphorylation and activation of the EGF-R. This activation may subsequently activate epidermal phospholipase at early time points after UVB exposure.