Int6, a new gene involved in the regulation of microtubule dynamics in Drosophila S2 cells

Gruppo di Ricerca: 
Renda F., Naim V., Bucciarelli E., Pellacani C., Palena A., Sharp D.J., Gatti M. and Somma M.P.
Attach English: 

The mitotic spindle is an extraordinarily dynamic machine that moves and segregates chromosomes during cell division. Spindle assembly and dynamics are mediated by a series of proteins that controls microtubule (MT) polymerization and depolymerization, MT stability and MT sliding, generating the forces necessary for chromosome segregation. Understanding the mechanisms underlying MT dynamics and spindle formation can provide a substantial contribution to the development of new cancer therapies.

 

In a recent RNAi-based screen we identified several new genes required for proper spindle assembly, including int6 thatencodes a component of the translation initiation complex that also interacts with both the 26S proteasome and the COP9 signalosome. Several published studies indicate that Int6 is a proto-oncogene implicated in various types of cancer, but its precise biological activity has not been defined. We found that RNAi-mediated depletion of Int6 in Drosophila S2 cells results in a metaphase arrest phenotype, with short spindles, elongated/distorted centromere/kinetochore regions and abnormally shaped centrosomes. Double RNAi experiments to simultaneously deplete both Int6 and a protein required for either spindle formation or metaphase-to-anaphase transition further suggested that Int6 is involved in the regulation of MT dynamics. Time-lapse imaging of Int6-depleted cells expressing tubulin-GFP indicated that they form a normal mitotic spindle but then remain arrested in metaphase. During metaphase arrest, the spindle length progressively decreases leading to a short and compact structure. FRAP analysis further suggested that Int6 activity is specifically required for MT plus-end dynamics at the spindle equator. Collectively, our results lead us to propose that Int6 controls the levels and/or the activities of MT-depolymerising motors by regulating protein degradation complexes such as the proteasome and the COP9 signalosome.

 

Anno del Convegno: 
2012

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