CD44 Proteolysis Increases CREB Phosphorylation and Sustains Proliferation of Thyroid Cancer Cells

Abstract

CD44 is a marker of cancer stem-like cells and epithelial-mesenchymal transition that is overexpressed in many cancer types, including thyroid carcinoma. At extracellular and intramembranous domains, CD44 undergoes sequential metalloprotease-and g-secretase-mediated proteolytic cleavage, releasing the intracellular protein fragment CD44-ICD, which translocates to the nucleus and activates gene transcription. Here, we show that CD44-ICD binds to the transcription factor CREB, increasing S133 phosphorylation and CREB-mediated gene transcription. CD44-ICD enhanced CREB recruitment to the cyclin D1 promoter, promoting cyclin D1 transcription and cell proliferation. Thyroid carcinoma cells harboring activated RET/PTC, RAS, or BRAF oncogenes exhibited CD44 cleavage and CD44-ICD accumulation. Chemical blockade of RET/PTC, BRAF, metalloprotease, or g-secretase were each sufficient to blunt CD44 processing. Furthermore, thyroid cancer cell proliferation was obstructed by RNA interference-mediated knockdown of CD44 or inhibition of g-secretase and adoptive CD44-ICD overexpression rescued cell proliferation. Together, these findings reveal a CD44-CREB signaling pathway that is needed to sustain cancer cell proliferation, potentially offering new molecular targets for therapeutic intervention in thyroid carcinoma. Cancer Res; 72(6);

Stress-Response Protein RBM3 Attenuates the Stem-like Properties of Prostate Cancer Cells by Interfering with CD44 Variant Splicing

“…On the other hand, CD44s has shown an inhibitory role during metastasis in prostate cancer (47); this, however, does not require the binding of prostate cancer cells to hyaluronan (48). The regulation of CD44-ICD on gene transcription has only been explored more recently (31,32). In the present study, we found that CD44v interfered with the tumor-suppressing function of CD44s by blocking its cleavage and, potentially, the consequent transcription of cyclin D1, which is a CD44-ICDinduced gene.…”

“…S3D). In contrast, when the expression of RBM3 in PC3 cells was induced under 32 C, the ratio of CD44v8-v10 to CD44s was decreased accordingly (Fig. 4G).…”

“…This results in shedding of the ecto-CD44 that, in turn, regulates cell-extracelluar matrix interaction, and release of the CD44 intracellular domain (CD44-ICD) that translocates to the nucleus and activates transcription of genes such as cyclin D1 (31,32). Indeed, the expression pattern of cyclin D1 is consistent with that of CD44s in cell colonies that formed in soft agar or in cells cultured at 32 C, indicating a potential correlation between CD44s function and transcription of cyclin D1 ( Supplementary Fig.…”

Induction and Analysis of Epithelial to Mesenchymal Transition

“…Different cell types can be compared pre-and post-EMT induction to obtain common expression signatures associated with EMT, such as the increase in phosphorylated CREB and ERK1/2 seen in both MCF7 and A549 EMT-induced cells. S133 phosphorylation of CREB stimulates DNA binding and has been shown to act downstream of TGF-β1-induced EMT 15 . ERK1/2 phosphorylation has also been shown to act downstream of TGF-β1-induced EMT 16 .…”

Targeting γ-secretase in breast cancer

“…58 These observations are corroborated by a recent study, which reported that CD44 ICD enhanced cyclic adenosine monophosphate response element-bindingmediated cyclin D1 transcription and, consequently, cell proliferation in thyroid tumor cells. 59 Most importantly, γ-secretase inhibition suppressed the proliferation of thyroid cancer cells, which could be reversed by ectopic expression of CD44 ICD. If these results could be replicated in breast cancer cells, it will undoubtedly provide a strong argument for using GSIs to achieve therapeutic benefits.…”