Regulation and subcellular localization of the microtubule‐destabilizing stathmin family phosphoproteins in cortical neurons

Abstract

Stathmin is a ubiquitous cytosolic phosphoprotein, preferentially expressed in the nervous system, and the generic element of a protein family that includes the neural-specific proteins SCG10, SCLIP, and RB3 and its splice variants, RB3' and RB3". All phosphoproteins of the family share with stathmin its tubulin binding and microtubule (MT)-destabilizing activities. To understand better the specific roles of these proteins in neuronal cells, we performed a comparative study of their expression, regulation, and intracellular distribution in embryonic cortical neurons in culture. We found that stathmin is highly expressed ( approximately 0.25% of total proteins) and uniformly present in the various neuronal compartments (cell body, dendrites, axon, growth cones). It appeared mainly unphosphorylated or weakly phosphorylated on one site, and antisera to specific phosphorylated sites (serines 16, 25, or 38) did not reveal a differential regulation of its phosphorylation among neuronal cell compartments. However, they revealed a subpopulation of cells in which stathmin was highly phosphorylated on serine 16, possibly by CaM kinase II also active in a similar subpopulation. The other proteins of the stathmin family are expressed about 100-fold less than stathmin in partially distinct neuronal populations, RB3 being detected in only about 20% of neurons in culture. In contrast to stathmin, they are each mostly concentrated at the Golgi apparatus and are also present along dendrites and axons, including growth cones. Altogether, our results suggest that the different members of the stathmin family have complementary, at least partially distinct functions in neuronal cell regulation, in particular in relation to MT dynamics.

The Microtubule Regulator Stathmin Is an Endogenous Protein Agonist for TLR3

“…Stathmin was expressed at comparable levels in all cell types. This localization of either protein is consistent with earlier reports (13,19,21). Previously, we reported that TLR3 is undetectable by immunohistochemistry in healthy control brains or noninflamed normal-appearing white matter of MS patients (13); our current data, as illustrated in Fig.…”

SCLIP Is Crucial for the Formation and Development of the Purkinje Cell Dendritic Arbor

“…In addition to their different distributions in the cerebellum, SCLIP and stathmin further display distinct intracellular localizations in PCs that might underlie their functional diversity. As expected from their previously characterized subcellular localization in neurons (Di Paolo et al, 1997;Gavet et al, 2002;Charbaut et al, 2005), stathmin has a homogeneous cytosolic distribution in the soma and dendrites (Ohkawa et al, 2007), whereas SCLIP specifically accumulates at the Golgi complex and vesicular structures in the principal trunk and secondary branches of dendrites during their outgrowth. It is thus tempting to speculate that the specific targeting of SCLIP in growing dendrites might be responsible for its crucial role in PC dendritic outgrowth during cerebellar development.…”

“…They have been originally identified for their capacity to integrate and relay intracellular signaling pathways (Sobel, 1991), at least in part through tubulin binding and the control of microtubule dynamics (Belmont and Mitchison, 1996;Curmi et al, 1997;Steinmetz et al, 2000;Charbaut et al, 2001;Ravelli et al, 2004). Whereas stathmin is ubiquitous and cytosolic, the other proteins are essentially expressed in the nervous system and localized at the Golgi complex and vesicular structures along neurite shafts and in growth cones (Di Paolo et al, 1997; Gavet et al, 2002;Charbaut et al, 2005). Their expression during development and their regional and cellular distribution in the brain are differently regulated .…”

Expression of Stathmin, a Developmentally Controlled Cytoskeleton-Regulating Molecule, in Demyelinating Disorders

“…Western blot analysis was performed by incubating nitrocellulose membrane with a monoclonal antibody recognizing MBP (MAb26) and with the rabbit polyclonal stathmin antibody (Calbiochem), raised against the last C-terminal aa 134 -149 of the molecule (Koppel et al, 1990). The detection of the phosphorylated forms of stathmin was obtained by Western blot analysis using specific antibodies [generated by A.S. and characterized in the study by Gavet et al (2002)] against phosphoserine S16, S25, or S38, used at a dilution of 1:20,000. Immunoreactive bands were identified with horseradish peroxidase-conjugated secondary antibodies, followed by chemiluminescence (Amersham).…”