Transforming growth factor-a (TGF-a)-induced proliferation and transforming growth factor-b (TGF-b)-mediated quiescence are intricately balanced in normal lung-tissue homeostasis but are deregulated during neoplastic progression of lung cancer. Here, we show that Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2), a novel MYCinteracting transcriptional modulator, responds to TGF-a induction and TGF-b suppression to orchestrate cellular proliferation and quiescence, respectively. Upon TGF-a induction, CITED2 was induced by MYC and further modulated MYC-mediated transcription in a feed-forward manner. CITED2 recruited p300 to promote MYC-p300-mediated transactivation of E2F3, leading to increased G1/S cell cycle progression. Moreover, CITED2 inhibited cellular quiescence by enhancing MYC-mediated suppression of p21 CIP1 . CITED2 interacted with histone deacetylase 1 (HDAC1) and potentiated MYC-HDAC1 complex formation. TGF-b stimulation provoked downregulation of CITED2, which abrogated MYC-HDAC1-mediated p21 CIP1 suppression, causing cellular quiescence. Ectopic CITED2 expression enhanced tumor growth in nude mice; furthermore, CITED2 knockdown caused tumor shrinkage and increased overall host mouse survival rates. Expression of CITED2/MYC/E2F3/ p21 CIP1 signaling molecules was associated with poor prognosis of lung cancer patients. Thus, CITED2 functions as a molecular switch of TGF-a and TGF-b-induced growth control, and MYC-CITED2 signaling axis provides a new index for predicting clinical outcome.

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