Smad7 palmitoylation by the S-acyltransferase zDHHC17 enhances its inhibitory effect on TGF-ß/Smad signaling.

Intracellular signaling by the pleiotropic cytokine transforming growth factor-ß (TGF-ß) is inhibited by Smad7 in a feedback control mechanism. The activity of Smad7 is tightly regulated by multiple post-translational modifications. Using resin-assisted capture and metabolic labeling methods, we show here that Smad7 is S-palmitoylated in mammary epithelial cell models that are widely studied because of their strong responses to TGF-ß and their biological relevance to mammary development and tumor progression. S-palmitoylation of Smad7 is mediated by zDHHC17, a member of a family of 23 S-acyltransferase enzymes. Moreover, we identified four cysteine residues (Cys202, Cys225, Cys415, and Cys417) in Smad7 as palmitoylation acceptor sites. S-palmitoylation of Smad7 on Cys415 and Cys417 promoted the translocation of Smad7 from the nucleus to the cytoplasm, enhanced the stability of the Smad7 protein, and enforced its inhibitory effect on TGF-ß-induced Smad transcriptional response. Thus, our findings reveal a new post-translational modification of Smad7, and highlight an important role of S-palmitoylation to enhance inhibition of TGF-ß/Smad signaling by Smad7.

Crosstalk between TGF-ß and EGF receptors via direct phosphorylation.

Aristidis Moustakas discusses work from Ye-Guang Chen and colleagues (https://doi.org/10.1083/jcb.202307138) on a new mechanism by which TGF-ß modulates HER2 signaling in mammary epithelia.

Unboxing the network among long non-coding RNAs and TGF-ß signaling in cancer.

Deeper analysis of molecular mechanisms arising in tumor cells is an unmet need to provide new diagnostic and therapeutic strategies to prevent and treat tumors. The transforming growth factor ß (TGF-ß) signaling has been steadily featured in tumor biology and linked to poor prognosis of cancer patients. One pro-tumorigenic mechanism induced by TGF-ß is the epithelial-to-mesenchymal transition (EMT), which can initiate cancer dissemination, enrich the tumor stem cell population, and increase chemoresistance. TGF-ß signals via SMAD proteins, ubiquitin ligases, and protein kinases and modulates the expression of protein-coding and non-coding RNA genes, including those encoding larger than 500 nt transcripts, defined as long non-coding RNAs (lncRNAs). Several reports have shown lncRNAs regulating malignant phenotypes by directly affecting epigenetic processes, transcription, and post-transcriptional regulation. Thus, this review aims to update and summarize the impact of TGF-ß signaling on the expression of lncRNAs and the function of such lncRNAs as regulators of TGF-ß signaling, and how these networks might impact specific hallmarks of cancer.