Akt kinase plays a central role in cell growth, metabolism and tumorigenesis. Although TRAF6 E3 ligase orchestrates IGF-1-mediated Akt ubiquitination and activation, it is unclear whether TRAF6 is involved in Akt activation by other growth factor receptors as well. Here we show that Akt ubiquitination is also induced by activation of ErbB receptors; unexpectedly, Skp2 SCF complex, but not TRAF6, is a critical E3 ligase for ErbB receptor-mediated Akt ubiquitination and membrane recruitment. Interestingly, Skp2 deficiency impairs Akt activation, Glut1 expression, glucose uptake and glycolysis, and breast cancer progression in various tumor models. Moreover, Skp2 overexpression correlates with Akt activation, breast cancer metastasis, and serves as a marker for poor prognosis in Her2-positive patients. Finally, we showed that Skp2 silencing sensitizes Her2-overexpressing tumors to Herceptin treatment. Our study suggests that distinct E3 ligases are utilized by diverse growth factors for Akt ubiquitination and activation.

RhoA GTPase plays a crucial role in numerous biological functions and is linked to cancer metastasis. However, the understanding of the molecular mechanism responsible for RhoA transcription is still very limited. Here we show that RhoA transcription is orchestrated by the Myc/Skp2/Miz1/p300 transcription complex. Skp2 cooperates with Myc to induce RhoA transcription by recruiting Miz1 and p300 to the RhoA promoter independently of SCF-Skp2 E3 ligase activity. Deficiency of this complex results in impairment in RhoA expression, cell migration, invasion, and breast cancer metastasis, recapitulating the phenotypes observed in RhoA knockdown, and RhoA restoration rescues the defect in cell invasion. Strikingly, the overexpression of Myc/Skp2/Miz1 complex is found in metastatic human cancers and correlated with RhoA expression. Our study provides great insight into how oncogenic Skp2 and Myc coordinate to induce RhoA transcription and establishes a novel SCF-Skp2 E3 ligase-independent function for oncogenic Skp2 in transcription and cancer metastasis.

Phosphaturic mesenchymal tumors typically cause paraneoplastic osteomalacia, chiefly as a result of FGF23 secretion. In a prior study, we identified FN1-FGFR1 fusion in 9 of 15 phosphaturic mesenchymal tumors. In this study, a total of 66 phosphaturic mesenchymal tumors and 7 tumors resembling phosphaturic mesenchymal tumor but without known phosphaturia were studied. A novel FN1-FGF1 fusion gene was identified in two cases without FN1-FGFR1 fusion by RNA sequencing and cross-validated with direct sequencing and western blot. Fluorescence in situ hybridization analyses revealed FN1-FGFR1 fusion in 16 of 39 (41%) phosphaturic mesenchymal tumors and identified an additional case with FN1-FGF1 fusion. The two fusion genes were mutually exclusive. Combined with previous data, the overall prevalence of FN1-FGFR1 and FN1-FGF1 fusions was 42% (21/50) and 6% (3/50), respectively. FGFR1 immunohistochemistry was positive in 82% (45/55) of phosphaturic mesenchymal tumors regardless of fusion status. By contrast, 121 cases of potential morphologic mimics (belonging to 13 tumor types) rarely expressed FGFR1, the main exceptions being solitary