IIp45 Inhibits Cell Migration through Inhibition of HDAC6

Abstract

IIp45 (aka MIIP) is a newly discovered gene whose protein product inhibits cell migration. HDAC6 is a class IIb deacetylase that specifically deacetylates ␣-tubulin, modulates microtubule dynamics, and promotes cell migration. A yeast two-hybrid assay using IIp45 as bait identified HDAC6 protein as a binding partner of IIp45. This physical interaction of the two functionally antagonistic proteins was confirmed by glutathione S-transferase pulldown assay and coimmunoprecipitation assay in human cells. Serial deletion constructs of HDAC6 were used to characterize the interaction of HDAC6 and IIp45, and this analysis found that the two catalytic domains of HDAC6 protein are required for IIp45 binding. We examined the protein expression patterns of IIp45 and HDAC6 in glioma tissues. Elevated protein levels of HDAC6 were found in high grade glioma samples, in contrast to the decreased protein expression of IIp45. The potential negative regulation of HDAC6 expression by IIp45 was confirmed in cell lines with altered IIp45 expression by constitutive overexpression or small interfering RNA knockdown. Protein turnover study revealed that overexpression of IIp45 significantly reduces the intracellular protein stability of endogenous HDAC6, indicating a possible mechanism for the negative regulation of HDAC6 by IIp45. Results from the HDAC activity assay demonstrated that overexpressed IIp45 effectively decreases HDAC6 activity, increases acetylated ␣-tubulin, and reduces cell migration. The increased cell migration resulting from siIIp45 knockdown was significantly reversed by co-transfection of siHDAC6. Thus, we report here for the first time a novel mechanism by which IIp45 inhibits cell motility through inhibition of HDAC6.Cell motility is important for normal tissue development and remodeling as well as for pathological conditions such as cancer invasion and metastasis (1, 2). Cell motility is controlled by well orchestrated programs that modulate the microtubule stabilization and destabilization cycles that permit cells to move efficiently (3). One of the key regulatory mechanisms of microtubule dynamics is acetylation of ␣-tubulin (4). Acetylation of protein lysine residues is a well recognized post-translational modification that modulates various pathways of cellular signal transduction. Protein acetylation is regulated by a number of acetyltransferases and deacetylases, which include the histone deacetylase (HDAC) 2 family (5). Among the 18 HDAC family members that have been reported in humans, HDAC6, classified as a type II histone deacetylase, is the only member that has two functional deacetylase domains and a zinc finger motif (6). Both catalytic domains are required for HDAC6 enzymatic activity (7). HDAC6 is also unique in that it is localized mainly in the cytoplasm and specifically deacetylates ␣-tubulin, the most abundant microtubule component, rather than histone proteins (8). In addition to ␣-tubulin, heat shock protein 90 (hsp90) and cortactin are two well recognized substrate proteins for HDAC6-mediat...

Rho-associated Coiled-coil Kinase (ROCK) Protein Controls Microtubule Dynamics in a Novel Signaling Pathway That Regulates Cell Migration

“…and invasion (36,37), whereas overexpression of HDAC6, which reduced tubulin acetylation, increased their invasiveness (38), thereby suggesting that aberrant tubulin acetylation may contribute to malignancies. Our data establish that overexpression of TPPP1 reduces cell migration and invasion, whereas its down-regulation increases cell migration and invasion.…”

Tubulin acetylation: responsible enzymes, biological functions and human diseases

“…a-Tubulin acetylation was shown to regulate breast cancer invasion [131]. Because invasion inhibitory protein 45 (IIp45) and G protein-coupled receptor kinase 2 (GRK2) modulate cell motility by interacting with HDAC6 [132,133], this deacetylase itself may also be involved in regulating cell migration.…”

Insulin-Like Growth Factor Binding Protein-2: A Possible Regulator of Invasive Growth in Glioblastoma

“…It may be possible that upregulated NF-κB in the absence of IIp45/MIIP also stimulates IGFBP2 transcription and eventually establishes an autocrine stimulation circuit for invasive growth. Moreover, recent studies have indicated that IIp45/MIIP also interacts with intracellular proteins, such as Cdc20 and histon deacetylase 6 (HDAC6), and inhibits glioma cell proliferation and migration (Ji et al, 2010;Wu et al, 2010). Therefore, interaction between IIp45/MIIP and intracellular IGFBP2 may occur in glioblastoma cells, which may attenuate the function of IIp45/MIIP and thereby may enhance the cellular proliferation and migration.…”