Biomedical subjects

Niovi Santama

Publications and source records attributed to Niovi Santama.

3 recordsLinked to original sources

PubMed2006

Motor protein KIFC5A interacts with Nubp1 and Nubp2, and is implicated in the regulation of centrosome duplication.

Inhibition of motor protein activity has been linked with defects in the formation of poles in the spindle of dividing cells. However, the molecular mechanisms underlying the functional relationship between motor activity and centrosome dynamics have remained uncharacterised. Here, we characterise KIFC5A, a mouse kinesin-like protein that is highly expressed in dividing cells and tissues, and is subject to developmental and cell-type-specific regulation. KIFC5A is a minus-end-directed, microtubule-dependent motor that produces velocities of up to 1.26 microm minute(-1) in gliding assays and possesses microtubule bundling activity. It is nuclear in interphase, localises to the centre of the two microtubule asters at the beginning of mitosis, and to spindle microtubules in later mitotic phases. Overexpression of KIFC5A in mouse cells causes the formation of aberrant, non-separated microtubule asters and mitotic arrest in a prometaphase-like state. KIFC5A knockdown partly rescues the phenotype caused by inhibition of plus-end-directed motor Eg5 by monastrol on the mitotic spindle, indicating that it is involved in the balance of forces determining bipolar spindle assembly and integrity. Silencing of KIFC5A also results in centrosome amplification detectable throughout the cell cycle. Supernumerary centrosomes arise primarily as a result of reduplication and partly as a result of cytokinesis defects. They contain duplicated centrioles and have the ability to organise microtubule asters, resulting in the formation of multipolar spindles. We show that KIFC5A interacts with nucleotide-binding proteins 1 and 2 (Nubp1 and Nubp2), which have extensive sequence similarity to prokaryotic division-site-determining protein MinD. Nubp1 and Nubp2 also interact with each other. Knockdown of Nubp1 or double knockdown of Nubp1 and Nubp2 (Nubp1&Nubp2) both phenocopy the KIFC5A silencing effect. These results implicate KIFC5A and the Nubp proteins in a common regulatory pathway involved in the control of centrosome duplication in mammalian cells.

Adenosine Triphosphatases↗

PubMed2005

Characterization of hCINAP, a novel coilin-interacting protein encoded by a transcript from the transcription factor TAFIID32 locus.

Coilin is a marker protein for the Cajal body, a subnuclear domain acting as a site for assembly and maturation of nuclear RNA-protein complexes. Using a yeast two-hybrid screen to identify coilin-interacting proteins, we have identified hCINAP (human coilin interacting nuclear ATPase protein), a nuclear factor of 172 amino acids with a P-loop nucleotide binding motif and ATPase activity. The hCINAP protein sequence is highly conserved across its full-length from human to plants and yeast and is ubiquitously expressed in all human tissues and cell lines tested. The yeast orthologue of CINAP is a single copy, essential gene. Tagged hCINAP is present in complexes containing coilin in mammalian cells and recombinant, Escherichia coli expressed hCINAP binds directly to coilin in vitro. The 214 carboxyl-terminal residues of coilin appear essential for the interaction with hCINAP. Both immunofluorescence and fluorescent protein tagging show that hCINAP is specifically nuclear and distributed in a widespread, diffuse nucleoplasmic pattern, excluding nucleoli, with some concentration also in Cajal bodies. Overexpression of hCINAP in HeLa cells results in a decrease in the average number of Cajal bodies per nucleus, consistent with it affecting either the stability of Cajal bodies and/or their rate of assembly. The hCINAP mRNA is an alternatively spliced transcript from the TAF9 locus, which encodes the basal transcription factor subunit TAFIID32. However, hCINAP and TAFIID32 mRNAs are translated from different ATG codons and use distinct reading frames, resulting in them having no identity in their respective protein sequences.

Adenosine Triphosphate↗

PubMed2004

Distribution and functions of kinectin isoforms.

Kinectin is an integral transmembrane protein on the endoplasmic reticulum, binding to kinesin, interacting with Rho GTPase and anchoring the translation elongation factor-1 complex. There has been debate on the specific role(s) of kinectin in different species and cell types. Here we identified 15 novel kinectin isoforms in the mouse nervous system, constituting a family of alternatively spliced carboxyl-terminal variants. Isoform expression is subject to cell type- and developmental stage-specific regulation. We raised specific antibodies to the kinectin variants to characterise their differential intracellular localisation and discovered that certain kinectin isoforms are found in axons where kinectin was previously believed to be absent. We also demonstrated in vivo by overexpression and RNA interference assay that kinectin is selectively involved in the transport of specific types of organelles. A 160 kDa kinectin species is mainly concentrated in the endoplasmic reticulum, anchored via its transmembrane domain and is essential for endoplasmic reticulum membrane extension. A 120 kDa kinectin species is specifically associated with mitochondria, and its interaction with kinesin was found to influence mitochondrial dynamics. These findings contribute to a more unified view of kinectin function. They suggest that different cellular processes use specific kinectin isoforms to mediate intracellular motility and targeting by transient interaction with different motor proteins or other binding partners.

Alternative Splicing↗