TPPP/p25 promotes tubulin assemblies and blocks mitotic spindle formation

Abstract

Recently, we isolated from bovine brain a protein, TPPP͞p25 and identified as p25, a brain-specific protein that induced aberrant tubulin assemblies. The primary sequence of this protein differs from that of other proteins identified so far; however, it shows high homology with p25-like hypothetical proteins sought via BLAST. Here, we characterized the binding of TPPP͞p25 to tubulin by means of surface plasmon resonance; the kinetic parameters are as follows: kon, 2.4 ؋ 10 4 M ؊1 ⅐s ؊1 ; koff, 5.4 ؋ 10 ؊3 s ؊1 ; and Kd, 2.3 ؋ 10 ؊7 M. This protein at substoichometric concentration promotes the polymerization of tubulin into double-walled tubules and polymorphic aggregates or bundles paclitaxel-stabilized microtubules as judged by quantitative data of electron and atomic force microscopies. Injection of bovine TPPP͞p25 into cleavage Drosophila embryos expressing tubulin-GFP fusion protein reveals that TPPP͞p25 inhibits mitotic spindle assembly and nuclear envelope breakdown without affecting other cellular events like centrosome replication and separation, microtubule nucleation by the centrosomes, and nuclear growth. GTP counteracts TPPP͞p25 both in vitro and in vivo.T he cytoplasm of eukaryotic cells contains an elaborate network of cytoskeletal elements, consisting of actin and intermediate filaments and microtubules (MTs) engaged in a variety of cell functions, such as the extension and guidance of neurons or the formation of mitotic spindles required for chromosomal segregation. The polymerization dynamics of tubulin to MTs is under strict control (1). Numerous proteins have been reported to interact with the MTs as positive regulators of MT assembly (microtubule-associated proteins), either by promoting the polymerization of tubulin or by stabilizing MTs (1, 2). Only a few proteins are known to act as destabilizers, such as Op18͞stathmin, katanin, and some kinesin-like proteins (1, 2). We have reported recently that the M1 isoform of pyruvate kinase and Dictyostelium discoideum phosphofructokinase inhibit tubulin polymerization or promote disassembly of the MTs to thread-like oligomers in vitro (3-5).Recently, from bovine brain, we isolated and identified a protein that we denoted TPPP͞p25 (6), which corresponded to p25 (NCBI accession no. 2498194). This protein is a heat stable, cationic protein that induces polymerization of tubulin into unusual forms or bundling of paclitaxel-stabilized MT. The TPPP͞p25 protein was partially copurified with a tau kinase (7). The bovine TPPP͞p25-coding gene has been cloned (8), and recently the human homologue of TPPP͞p25 was cloned and mapped to the p15.3 region of chromosome 5. The identity between the bovine and human TPPP͞p25 proteins is 90% (9). This protein was also described as p24, a heat-resistant glycogen synthase kinase-3 inhibitor (10). It is important to note that TPPP͞p25 differs completely from the extensively characterized protein p25, which is a truncated form of p35 that deregulates cyclin-dependent kinase-5 activity by causing prolonged activation and m...

Tubulin Polymerization-promoting Protein (TPPP/p25α) Promotes Unconventional Secretion of α-Synuclein through Exophagy by Impairing Autophagosome-Lysosome Fusion

“…The tendency of ␣-synuclein to form cytosolic aggregates is influenced by a number of other proteins, including synphilin-1 (22), protein interacting with NIMA 1 (PIN-1) (23), and TPPP/ p25␣ (hereafter referred to as p25␣) (24). The p25␣ protein binds to microtubules and by doing so lowers their plus-end growth rate and protects them from depolymerization (25)(26)(27). In addition, p25␣ potently stimulates aggregation of ␣-synuclein in vitro and localizes to Lewy bodies in vivo (24,28).…”

Tubulin polymerization‐promoting protein family member 3, Tppp3, is a specific marker of the differentiating tendon sheath and synovial joints

“…One gene identified in this screen was Tppp3, a member of the family of Tubulin polymerization promoting proteins (Vincze et al, 2006). Tppp/P25 is a brain-specific protein that induces tubulin polymerization and microtubule bundling (Tirian et al, 2003). Tppp/p25 belongs to a group of intrinsically unstructured proteins that was extensively studied in recent years (Dunker et al, 2002;Orosz et al, 2004), and shows effects on tubulin polymerization both in vitro and in transfected cells.…”

On the tubulin polymerization promoting proteins of zebrafish

“…Its first member, tubulin polymerization promoting protein (TPPP or TPPP1) was first isolated from bovine brain [2] and later found to promote tubulin polymerization and stabilization of microtubules [3,4]. There are three TPPP paralogous genes in human, TPPP1, TPPP2 and TPPP3 (TPPP/p25, TPPP2/p18 and TPPP3/p20 at protein level) [5].…”