Protein 4.1 R-135 Interacts with a Novel Centrosomal Protein (CPAP) Which Is Associated with the γ-Tubulin Complex

Abstract

Using a yeast two-hybrid system, we isolated a novel human centrosomal protein, CPAP (centrosomal P4.1-associated protein), which specifically interacts with the head domain of the 135-kDa protein 4.1R isoform (4.1R-135). Sequence analysis revealed that the carboxyl terminus of CPAP has 31.3% amino acid identity with human Tcp-10 (a t-complex responder gene product). Interestingly, most of the sequence identity is restricted to two conserved regions. One carries a leucine zipper, which may form a series of heptad repeats involved in coiled-coil formation; the other contains unusual glycine repeats with unknown function. Immunofluorescence analysis revealed that CPAP and ␥-tubulin are localized within the centrosome throughout the cell cycle. CPAP cosediments with ␥-tubulin in sucrose gradients and coimmunoprecipitates with ␥-tubulin, indicating that CPAP is a part of the ␥-tubulin complex. Furthermore, functional analysis revealed that CPAP is localized within the center of microtubule asters and may participate in microtubule nucleation. The formation of microtubule asters was significantly inhibited by anti-CPAP antibody. Together, these observations indicate that CPAP may play an important role in cell division and centrosome function.

DNA damage induce γ-tubulin–RAD51 nuclear complexes in mammalian cells

“…It has been reported to be a constituent of g-TuSCs and g-TuRCs, the soluble complexes involved in microtubule nucleation (Wiese and Zheng, 1999). However, g-tubulin interacts with other centrosomal proteins that are absent from the gTuRCs but are potentially involved in g-tubulin polar recruitment and/or nucleation activity (Wiese and Zheng, 1999;Hung et al, 2000;Takahashi et al, 2002;Casenghi et al, 2003) or centrosome cohesion (Thompson et al, 2004). Moreover, this protein has been described in other complexes containing modification enzymes like kinases (Feng et al, 1999;Kukharskyy et al, 2004) or ubiquitin E3 ligases (Zhao et al, 2003;Starita et al, 2004).…”

Stat5 in the mammary gland: Controlling normal development and cancer

“…This protein is expressed predominantly in the cytoplasm with much lower levels in the nucleus, mainly in the centrosome (Hung et al, 2000). It interacts with Stat5a and Stat5b independent of their phosphorylation status, but not with Stat1 or Stat3.…”

Centrosomal P4.1-associated Protein Is a New Member of Transcriptional Coactivators for Nuclear Factor-κB

“…The antibodies used in these experiments were specific for FLAG, RelA (antibody F-6), and ␣-tubulin (antibody-1, Calbiochem). The rabbit antiserum against CPAP was kindly provided from Dr. T. K. Tang (Institute of Biomedical Sciences, Taipei, Taiwan, Republic of China) (22).…”

“…In a yeast two-hybrid screen using the N terminus of RelA as bait, we identified a novel RelA-interacting factor, centrosomal P4.1-associated protein (CPAP). CPAP was previously identified by virtue of its interaction with the cytoskeletal protein 4.1R-135 (22). Although CPAP appears to be a component of the centrosomal complex, the majority of CPAP is found in soluble fractions, mainly in the cytoplasm and a small portion in the nucleus (22,23).…”

“…CPAP was previously identified by virtue of its interaction with the cytoskeletal protein 4.1R-135 (22). Although CPAP appears to be a component of the centrosomal complex, the majority of CPAP is found in soluble fractions, mainly in the cytoplasm and a small portion in the nucleus (22,23). In addition, it was previously reported that CPAP interacts with STAT5 and enhances STAT5-mediated transcription (23), although the mechanism by which this occurs remains unclear.…”