Abeda Mulla

Post-translational modification plays an essential role in the translocation of annexin A1 from the cytoplasm to the cell surface

Annexin A1 (ANXA1) has an important role in cell‐cell communication in the host defense and neuroendocrine systems. In both systems, its actions are exerted extracellularly via membrane‐bound receptors on adjacent sites after translocation of the protein from the cytoplasm to the cell surface of adjacent cells. This study used molecular, microscopic, and pharmacological approaches to explore the mechanisms underlying the cellular exportation of ANXA1 in TtT/GF (pituitary folliculo‐stellate) cells. LPS caused serine‐phosphorylation of ANXA1 (ANXA1‐S27‐PO4) and translocation of the phosphorylated protein to the cell membrane. The fundamental requirement of phosphorylation for membrane translocation was confirmed by immunofluorescence microscopy on cells transfected with wild‐type or mutated (S27/A) ANXA1 constructs tagged with enhanced green fluorescence protein. The trafficking of ANXA1‐S27‐PO4 to the cell surface was dependent on PI3‐kinase and MAP‐kinase. It also required HMG‐coenzyme A and myristoylation. The effects of HMG‐coenzyme A blockade were overcome by mevalonic acid (the product of HMG‐coen‐zyme A) and farnesyl‐pyrophosphate but not by geranyl‐geranylpyrophosphate or cholesterol. Together, these results suggest that serine‐27 phosphorylation is essential for the translocation of ANXA1 across the cell membrane and also identify a role for isoprenyl lipids. Such lipids could target consensus sequences in ANXA1. Alternatively, they may target other proteins in the signal transduction cascade (e.g., transporters).—Solito, E., Christian, H. C., Festa, M., Mulla, A., Tierney, T., Flower, R. J., Buckingham, J. C. Post‐transla‐tional modification plays an essential role in the translocation of annexin A1 from the cytoplasm to the cell surface. FASEB J. 20, E677–E687 (2006)

Expression, subcellular localization and phosphorylation status of annexins 1 and 5 in human pituitary adenomas and a growth hormone-secreting carcinoma

objective  Annexin 1 (ANXA1), a 37‐kDa protein, plays an important role as a mediator of glucocorticoid action in the anterior pituitary gland and has been implicated in the processes of tumorigenesis in a number of other tissues. As a prelude to examining the potential role of ANXA1 in the pathophysiology of pituitary tumours, this study examined the expression, phosphorylation status and distribution of ANXA1 and the closely related protein, annexin 5 (ANXA5), in a series of pituitary adenomas and in two carcinomas.