SMURF1 and head and neck squamous cell carcinoma: In support of this idea, we determined that HNSCC sphere cells deactivate BMP signaling intracellularly by upregulating SMURF1, leading to decreased levels of pSMAD1/5/8 and ID1, the canonical BMP receptor signal transducer [30, 58, 59] and BMP signaling target gene [26, 60], respectively.