Primary Megakaryocytes Reveal a Role for Transcription Factor NF-E2
Primary Megakaryocytes Reveal a Role for Transcription Factor NF-E2 in Integrin aIIbb3 Signaling Masamichi Shiraga,* Alec Ritchie,* Sallouha Aidoudi,* Veronique Baron,* David Wilcox,‡ Gilbert White,§ Belen Ybarrondo,i George Murphy,¶ Andrew Leavitt,¶ and Sanford Shattil* *Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037; ‡Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226; §Department of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599; iPharMingen, Inc., San Diego, California 92139; and ¶Department of Laboratory Medicine, The University of California at San Francisco, San Francisco, California 94143 Abstract. Platelet integrin aIIbb3 responds to intracel- cient in the transcription factor NF-E2 failed to bind lular signals by binding fibrinogen and triggering cy- fibrinogen in response to agonists, despite normal toskeletal reorganization, but the mechanisms of surface expression of aIIbb3. Furthermore, while aIIbb3 signaling remain poorly understood. To better megakaryocytes from wild-type mice spread on immo- understand this process, we established conditions to bilized fibrinogen and exhibited filopodia, lamellipodia study aIIbb3 signaling in primary murine megakaryo- and Rho-dependent focal adhesions and stress fibers, cytes. Unlike platelets, these platelet precursors are NF-E2–deficient megakaryocytes adhered poorly. amenable to genetic manipulation. Cytokine-stimu- These studies establish that agonist-induced activation lated bone marrow cultures produced three arbitrary of aIIbb3 is controlled by NF-E2–regulated signaling populations of aIIbb3-expressing cells with increasing pathways that mature late in megakaryocyte develop- size and DNA ploidy: small progenitors, intermediate- ment and converge at the b3 cytoplasmic tail. Mega- size young megakaryocytes, and large mature mega- karyocytes provide a physiologically relevant and karyocytes.
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