SMURF1 and neoplasm: In this model, SLU7-mediated circCAPG is identified to encode a polypeptide CAPG-171aa which promotes tumor growth by disrupting the binding of serine/threonine kinase 38 (STK38) to SMAD-specific E3 ubiquitin protein ligase 1 (SMURF1) and thereby preventing MEKK2 ubiquitination and proteasomal degradation.