An essential link to mammary cancer?

Gene network signaling in hormone responsiveness modifies apoptosis and autophagy in breast cancer cells

Resistance to endocrine therapies, whether de novo or acquired, remains a major limitation in the ability to cure many tumors that express detectable levels of the estrogen receptor alpha protein (ER). While several resistance phenotypes have been described, endocrine unresponsiveness in the context of therapy-induced tumor growth appears to be the most prevalent. The signaling that regulates endocrine resistant phenotypes is poorly understood but it involves a complex signaling network with a topology that includes redundant and degenerative features. To be relevant to clinical outcomes, the most pertinent features of this network are those that ultimately affect the endocrine-regulated components of the cell fate and cell proliferation machineries. We show that autophagy, as supported by the endocrine regulation of monodansylcadaverine staining, increased LC3 cleavage, and reduced expression of p62/SQSTM1, plays an important role in breast cancer cells responding to endocrine therapy. We further show that the cell fate machinery includes both apoptotic and autophagic functions that are potentially regulated through integrated signaling that flows through key members of the BCL2 gene family and beclin-1 (BECN1). This signaling links cellular functions in mitochondria and endoplasmic reticulum, the latter as a consequence of induction of the unfolded protein response. We have taken a seed-gene approach to begin extracting critical nodes and edges that represent central signaling events in the endocrine regulation of apoptosis and autophagy. Three seed nodes were identified from global gene or protein expression analyses and supported by subsequent functional studies that established their abilities to affect cell fate. The seed nodes of nuclear factor kappa B (NFkappaB), interferon regulatory factor-1 (IRF1), and X-box binding protein-1 (XBP1)are linked by directional edges that support signal flow through a preliminary network that is grown to include key regulators of their individual function: NEMO/IKKgamma, nucleophosmin and ER respectively. Signaling proceeds through BCL2 gene family members and BECN1 ultimately to regulate cell fate.

Serine-phosphorylated STAT1 is a prosurvival factor in Wilms' tumor pathogenesis

Wilms' tumor (WT), one of the most common pediatric solid cancers, arises in the developing kidney as a result of genetic and epigenetic changes that lead to the abnormal proliferation and differentiation of the metanephric blastema. As activation of signal transducers and activators of transcription (STATs) plays an important role in the maintenance/growth and differentiation of the metanephric blastema, and constitutively activated STATs facilitate neoplastic behaviors of a variety of cancers, we hypothesized that dysregulation of STAT signaling may also contribute to WT pathogenesis. Accordingly, we evaluated STAT phosphorylation patterns in tumors and found that STAT1 was constitutively phosphorylated on serine 727 (S727) in 19 of 21 primary WT samples and two WT cell lines. An inactivating mutation of S727 to alanine reduced colony formation of WT cells in soft agar by more than 80% and induced apoptosis under conditions of growth stress. S727-phosphorylated STAT1 provided apoptotic resistance for WT cells via upregulation of expression of the heat-shock protein (HSP)27 and antiapoptotic protein myeloid cell leukemia (MCL)-1. The kinase responsible for STAT1 S727 phosphorylation in WT cells was identified based upon the use of selective inhibitors as protein kinase CK2, not p38, MAP-kinase kinase (MEK)1/2, phosphatidylinositol 3'-kinase, protein kinase C or Ca/calmodulin-dependent protein kinase II (CaMKII). The inhibition of CK2 blocked the anchorage-independent growth of WT cells and induced apoptosis under conditions of growth stress. Our findings suggest that serine-phosphorylated STAT1, as a downstream target of protein kinase CK2, plays a critical role in the pathogenesis of WT and possibly other neoplasms with similar STAT1 phosphorylation patterns.