5216

PFN1

profilin 1;PFN1;profilin 1

epididymis tissue protein Li 184a|profilin I|profilin-1

17p13.3

protein-coding

Profilin1 (Pfn1), a ubiquitously expressed actin-binding protein, has an indispensable role in migration and proliferation of normal cells. Seemingly contrary to its essential cellular functions, Pfn1's expression is downregulated in breast cancer, the significance of which is unclear. In this study, expression profiling of Pfn1 in human breast cancer specimens correlates lower Pfn1 expression levels with propensity to metastasize. Xenograft experiments further establish a causal relationship between loss of Pfn1 expression and increased dissemination of breast cancer cells (BCCs) from the primary mammary tumor. BCCs exhibit a hyperinvasive phenotype (marked by matrix metalloproteinase-9 upregulation, faster invasion through collagen matrix) and acquire increased proficiency to transmigrate through endothelial barrier (an obligatory step for vascular dissemination) when Pfn1 expression is suppressed. In Pfn1-deficient cells, hyperinvasiveness involves a phosphatidylinositol 3-kinase-PI(3,4)P2 signaling axis while augmented transendothelial migration occurs in a vascular endothelial growth factor-dependent manner. Contrasting these dissemination promoting activities, loss of Pfn1, however, dramatically inhibits metastatic outgrowth of disseminated BCCs, suggesting that Pfn1 has a key role in the metastatic colonization process. In summary, this study shows that Pfn1 has a dichotomous role in early vs late steps of breast cancer metastasis.

Profilin1 (Pfn1) is a key mediator of actin polymerization and regulates cell migration. Low expression of Pfn1 is implicated in tumorigenesis of various cancers, including breast cancer. The regulatory mechanism behind Pfn1 levels has not yet been elucidated. In the present study, we find that Pfn1 is poly-ubiquitinated in human cell lines, and a portion of poly-ubiquitinated Pfn1 is regulated in a proteasome-dependent manner. C-terminus of Hsc70-interacting protein (CHIP), a co-chaperone E3 ligase, interacts with and ubiquitinates Pfn1, targeting it for proteasome-dependent degradation. Depletion of CHIP stabilizes Pfn1, suggesting that CHIP functions as a major E3 ligase for Pfn1. Stable expression of wild-type CHIP in the breast cancer cell line MDA-MB231 yielded downregulation of Pfn1 and enhanced cell migration. Pfn1 overexpression in MDA-MB231 cells expressing wild-type CHIP suppressed the enhanced cell migration. Taken together, our results demonstrate that CHIP regulates Pfn1 levels as an E3 ligase, and possibly plays a role in cell migration and metastasis of breast cancer.

Previous studies have shown that all-trans retinoic acid (ATRA) suppresses growth of hepatocarcinoma cell in vitro. To understand the underlying mechanisms, we investigated the protein expression profiles by 2-DE in hepatocarcinoma cell line SMMC-7721 treated with ATRA. Our results reveal that six proteins were differently expressed in response to ATRA. Using MS and database searching, they were identified as profilin 1, phosphoglycerate kinase 1, RuvB-like 1, alpha-enolase, pyridoxal kinase and F-actin capping protein. We selected the up-regulated protein, profilin 1 (PFN1), for further studies. The PFN1 expression was increased in response to ATRA in a dose- and time-dependent manner. The PFN1 expression was reduced dramatically in four hepatoma cell lines compared to L02 cell line of non-tumor origin. The PFN1 expression was also examined in 4 cases of primary hepatocarcinoma tissues by Western blot and 30 cases by tissues microarray. It was found that the protein level of PFN1 was lower in hepatocarcinoma tissues compared to that in the adjacent tissues. Similar to ATRA, overexpression of PFN1 led to inhibition of cell proliferation and migration. Furthermore, RNAi-based PFN1 knockdown could rescue the inhibitory effect of ATRA on cell proliferation and migration. In conclusion, ATRA inhibited cell proliferation and migration through up-regulation of PFN1.