Geneeskundige Stichting Koningin Elisabeth ... - GSKE - FMRE

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tion forming Ins(1,3,4,5)P 4 and Ins(1,4,5,6)P 4. A role of this multikinase in nuclear mRNA
export was recently described (Saiardi et al., 2000). None of these enzymes appears to specifically
produce Ins(1,3,4,5)P 4 as shown for the A and B forms of mammalian Ins(1,4,5)P 3 3kinases.
In mammalian systems, no phosphorylation at the 6-position (which would form
Ins(1,4,5,6)P 4) has ever been observed.
There are hints in the literature that the family of Ins(1,4,5)P 3 3-kinases may be more diverse.
In human platelets, rat thymus or thyroid cells, the Ins(1,4,5)P 3 3-kinase appears to run on
SDS gels as higher Mr protein(s) as compared to 3-kinases A and B. We have now reported
the sequence and expression of a third mammalian Ins(1,4,5)P 3 3-kinase (3-kinase C) that
demonstrates enzymatic activity when expressed in E. coli or COS-7 cells. This enzyme is rather
ubiquitous based on Northern blot analysis. We show for the first time an inhibition of activity
by calcium measured on transfected COS-7 cells suggesting a different mode of Ins(1,3,4,5)P 4
production in intact cells as compared to the A and B isoforms expressing cells. Depending on
the isoenzyme expression, Ins(1,3,4,5)P 4 production in various cells is tightly controlled
(Dewaste et al., 2000).
Identification of SHIP2 in Neurospheres (Muraille et al., submitted)
In 1997, we reported the cloning of a cDNA encoding human polyphosphatase 5-phosphatase
SHIP2 (Pesesse et al., 1997). SHIP2 contains one N-terminal SH2 domain, a catalytic
5-phosphatase domain in the central part , proline-rich regions, a NPXY motif, and a C-terminal
SAM domain. By Northern and Western blotting SHIP2 was demonstrated to be expressed
in different region of mouse brain (cortex, cerebellum, astrocytes...) (Muraille et al., 1999 ;
Kudo et al., 2000).
We conducted a study in collaboration with Prof Shiffmann (Laboratory of
Neurophysiology, ULB) in order to map the SHIP2 in brain. We demonstrated that SHIP2 mRNA
was highly expressed in the ventricular zone at early embryonic stages and subventricular zones
at latter stages of brain and spinal cord and in the sympathetic chain .No expression was seen
in differentiated fields. The restricted expression was maintained from E11.5 to birth. In the
periphery, large expression was detected in muscle and kidney and moderate expression in thyroid,
pituitary gland, digestive system and bone. In the adult brain, SHIP2 was mainly restricted
in structures containing neural stem cells such as the anterior subventricular zones and the
rostral migratory stream and the olfactory tubercle. We have shown directly by Western blotting
using a SHIP2 antibody the expression of the protein in proliferating neurospheres in culture
in contrast to non proliferating differentiated neurosheres (in collaboration with Bernard
Rogister). The data therefore suggest a role of SHIP2 in proliferating rather than in differentiating
events (Muraille et al., submitted).
The protein partners of SHIP2 in brain (identification by a yeast two hybrid screening in human brain)
By these different domains, SHIP2 is able to interact with different proteins and to organize
the cellular response to stimuli. By its SH2 domain, SHIP2 binds phosphorylated tyrosins of
the ITIM (immunoreceptor tyrosine-based inhibitor) motif of FcγRIIB, inhibiting the B lymphocytes