The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. This family includes EGFR/ErbB1/HER1, ErbB2/HER2/Neu ErbB3/HER3, and ErbB4/ HER4. For many years it was believed that EGFR plays a minor role in the development and progression of breast malignancies. However, recent findings have led investigators to revisit these beliefs. Here we will review these findings and propose roles that EGFR may play in breast malignancies. In particular, we will discuss the potential roles that EGFR may play in triplenegative tumors, resistance to endocrine therapies, maintenance of stem-like tumor cells, and bone metastasis. Thus, we will propose the contexts in which EGFR may be a therapeutic target.

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Cyclic AMP produced from membrane receptor complex bound adenylyl cyclases is protective in corneal endothelial cells (CEC). CEC also express soluble adenylyl cyclase (sAC), which is localized throughout the cytoplasm. When activated by HCO(3)(-), cAMP concentration ([cAMP]) increases by ∼50%. Here we ask if cAMP produced from sAC is also protective. We examined the effects of HCO(3)(-), pH, phosphodiesterase 4 inhibition by rolipram, sAC inhibition by 2HE (2-hydroxyestradiol), and sAC small interfering RNA (siRNA) knockdown on basal and staurosporine-mediated apoptosis. HCO(3)(-) (40 mM) or 50 μM rolipram raised [cAMP] to similar levels and protected endothelial cells by 50% relative to a HCO(3)(-)-free control, whereas 2HE, which decreased [cAMP] by 40%, and H89 (PKA inhibitor) doubled the apoptotic rate. sAC expression was reduced by two-thirds in the absence of HCO(3)(-) and was reduced to 15% of control by sAC siRNA. Protection by HCO(3)(-) was eliminated in siRNA-treated cells. Similarly, caspase-3 activity and cytochrome c release were reduced by HCO(3)(-) and enhanced by 2HE or siRNA. Analysis of percent annexin V+ cells as a function of [cAMP] revealed an inverse, nonlinear relation, suggesting a protective threshold [cAMP] of 10 pmol/mg protein. Relative levels of phosphorylated cAMP response element binding protein and phosphorylated Bcl-2 were decreased in CEC treated with 2HE or siRNA, suggesting that HCO(3)(-)-dependent endogenous sAC activity can mobilize antiapoptotic signal transduction. Overall, our data suggest a new role for sAC in endogenous cellular protection.

The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is present on the apical membrane of corneal endothelial cells. Increasing intracellular [cAMP] with forskolin stimulates an NPPB and glibenclamide-inhibitable apical Cl -and HCO 3 -permeability. To definitively determine that the increased permeability is dependent on CFTR, we used an siRNA knockdown approach. Apical Cl -and HCO 3 -permeability and steady-state HCO 3 -flux were measured in the presence or absence of forskolin using cultured bovine corneal endothelial cells that were transfected with CFTR siRNA or a scrambled sequence control. CFTR protein expression was reduced by ∼80% in CFTR siRNA treated cultures. Forskolin (10 μM) increased apical chloride permeability by 7 fold, which was reduced to control level in siRNA treated cells. CFTR siRNA treatment had no effect on baseline apical chloride permeability. Apical HCO 3 -permeability was increased 2 fold by 10 μM forskolin, which was reduced to control level in siRNA treated cultures. Similarly, there was no effect on baseline apical HCO 3 -permeability by knocking down CFTR expression. The steady-state apicalbasolateral pH gradient (ΔpH) at four hours in control cultures was increased ∼2.5 fold by forskolin. In CFTR siRNA treated cells, the baseline ΔpH was similar to control, however forskolin did not have a significant effect. We conclude that forskolin induced increases in apical HCO 3 -permeability in bovine corneal endothelium requires CFTR. However, CFTR does not have a major role in determining baseline apical chloride or HCO 3 -permeability.The corneal endothelium is responsible for maintaining the hydration and transparency of the cornea by counteracting the fluid imbibition properties of the glycosaminoglycan rich stroma. Numerous studies have shown that this process is dependent on the presence of HCO 3 -and slowed by inhibition of carbonic anhydrase activity (Hodson 1971;Barfort and Maurice 1974;Fischbarg and Lim 1974;Hodson 1974;Kuang et al. 1990;Riley et al. 1995). The endothelium develops a small apical side negative transendothelial potential (0.5 mV) that is significantly reduced by HCO 3 -withdrawal or by carbonic anhydrase inhibitors (Fischbarg 1972;Barfort and Maurice 1974;Fischbarg and Lim 1974;Hodson et al. 1977). Corneal swelling is also induced by the Na + /K + ATPase inhibitor ouabain, indicating that the endothelial pump involves active transport.HCO 3 -uptake at the basolateral (stromal) membrane has been identified as being predominantly via the 1Na + :2HCO 3 -cotransporter (NBCe1) (Sun et al. 2000;Sun and Bonanno 2003). A recent study showed that siRNA knockdown of NBC significantly reduced basolateral HCO 3 -permeability and eliminated net basolateral to apical fluxes (Li et al. 2005). Interestingly, studies using cultured cells indicate that basolateral HCO 3 -permeability is 3-4 times greater than apical permeability (Bonanno et al. 1999). The low HCO 3 -permeability of the apical membrane suggests that it is rate limiting for HCO 3 -fluxes and tha...

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