Previous work demonstrated that the extracellular domain of CD44 can be cleaved by membrane-associated proteases, regulating the interaction between CD44 and the extracellular matrix. Okamoto et al. identified a subsequent proteolytic cleavage that releases a fragment of the CD44 intracellular domain (CD44ICD). This fragment translocates to the nucleus, where it activates transcription from the TPA-responsive transcriptional regulation elements found in front of a variety of cellular genes. CD44ICD overexpression also induces CD44 mRNA expression, suggesting a feedback mechanism to regulate CD44 levels. In addition to illuminating the mechanism of CD44 signaling, the new work provides the first example of an adhesion molecule using a type of signal transduction first described for Notch, in which a cleavage fragment of a membrane receptor serves as a transcriptional activator. ▪

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