ErbB4 promotes malignant peripheral nerve sheath tumor pathogenesis via Ras-independent mechanisms.

BACKGROUND: We have found that erbB receptor tyrosine kinases drive Ras hyperactivation and growth in NF1-null malignant peripheral nerve sheath tumors (MPNSTs). However, MPNSTs variably express multiple erbB receptors with distinct functional characteristics and it is not clear which of these receptors drive MPNST pathogenesis. Here, we test the hypothesis that altered erbB4 expression promotes MPNST pathogenesis by uniquely activating key cytoplasmic signaling cascades. METHODS: ErbB4 expression was assessed using immunohistochemistry, immunocytochemistry, immunoblotting and real-time PCR. To define erbB4 functions, we generated mice that develop MPNSTs with floxed Erbb4 alleles (P0-GGFß3;Trp53+/-;Erbb4flox/flox mice) and ablated Erbb4 in these tumors. MPNST cell proliferation and survival was assessed using 3H-thymidine incorporation, MTT assays, Real-Time Glo and cell count assays. Control and Erbb4-null MPNST cells were orthotopically xenografted in immunodeficient mice and the growth, proliferation (Ki67 labeling), apoptosis (TUNEL labeling) and angiogenesis of these grafts was analyzed. Antibody arrays querying cytoplasmic kinases were used to identify erbB4-responsive kinases. Pharmacologic or genetic inhibition was used to identify erbB4-responsive kinases that drive proliferation. RESULTS: Aberrant erbB4 expression was evident in 25/30 surgically resected human MPNSTs and in MPNSTs from genetically engineered mouse models (P0-GGFß3 and P0-GGFß3;Trp53+/- mice); multiple erbB4 splice variants that differ in their ability to activate PI3 kinase and nuclear signaling were present in MPNST-derived cell lines. Erbb4-null MPNST cells demonstrated decreased proliferation and survival and altered morphology relative to non-ablated controls. Orthotopic allografts of Erbb4-null cells were significantly smaller than controls, with reduced proliferation, survival and vascularization. ERBB4 knockdown in human MPNST cells similarly inhibited DNA synthesis and viability. Although we have previously shown that broad-spectrum erbB inhibitors inhibit Ras activation, Erbb4 ablation did not affect Ras activation, suggesting that erbB4 drives neoplasia via non-Ras dependent pathways. An analysis of 43 candidate kinases identified multiple NRG1ß-responsive and erbB4-dependent signaling cascades including the PI3K, WNK1, STAT3, STAT5 and phospholipase-Cγ pathways. Although WNK1 inhibition did not alter proliferation, inhibition of STAT3, STAT5 and phospholipase-Cγ markedly reduced proliferation. CONCLUSIONS: ErbB4 promotes MPNST growth by activating key non-Ras dependent signaling cascades including the STAT3, STAT5 and phospholipase-Cγ pathways. ErbB4 and its effector pathways are thus potentially useful therapeutic targets in MPNSTs.

PINK1/Parkin Influences Cell Cycle by Sequestering TBK1 at Damaged Mitochondria, Inhibiting Mitosis.

PINK1 and Parkin are established mediators of mitophagy, the selective removal of damaged mitochondria by autophagy. PINK1 and Parkin have been proposed to act as tumor suppressors, as loss-of-function mutations are correlated with enhanced tumorigenesis. However, it is unclear how PINK1 and Parkin act in coordination during mitophagy to influence the cell cycle. Here we show that PINK1 and Parkin genetically interact with proteins involved in cell cycle regulation, and loss of PINK1 and Parkin accelerates cell growth. PINK1- and Parkin-mediated activation of TBK1 at the mitochondria during mitophagy leads to a block in mitosis due to the sequestration of TBK1 from its physiological role at centrosomes during mitosis. Our study supports a diverse role for the far-reaching, regulatory effects of mitochondrial quality control in cellular homeostasis and demonstrates that the PINK1/Parkin pathway genetically interacts with the cell cycle, providing a framework for understanding the molecular basis linking PINK1 and Parkin to mitosis.