Member Of ADP-ribosylation Factor Family Research Articles

Membrane trafficking alterations in breast cancer progression.

Breast cancer (BC) is the most common type of cancer in women, and remains one of the major causes of death in women worldwide. It is now well established that alterations in membrane trafficking are implicated in BC progression. Indeed, membrane trafficking pathways regulate BC cell proliferation, migration, invasion, and metastasis. The 22 members of the ADP-ribosylation factor (ARF) and the >60 members of the rat sarcoma (RAS)-related in brain (RAB) families of small GTP-binding proteins (GTPases), which belong to the RAS superfamily, are master regulators of membrane trafficking pathways. ARF-like (ARL) subfamily members are involved in various processes, including vesicle budding and cargo selection. Moreover, ARFs regulate cytoskeleton organization and signal transduction. RABs are key regulators of all steps of membrane trafficking. Interestingly, the activity and/or expression of some of these proteins is found dysregulated in BC. Here, we review how the processes regulated by ARFs and RABs are subverted in BC, including secretion/exocytosis, endocytosis/recycling, autophagy/lysosome trafficking, cytoskeleton dynamics, integrin-mediated signaling, among others. Thus, we provide a comprehensive overview of the roles played by ARF and RAB family members, as well as their regulators in BC progression, aiming to lay the foundation for future research in this field. This research should focus on further dissecting the molecular mechanisms regulated by ARFs and RABs that are subverted in BC, and exploring their use as therapeutic targets or prognostic markers.

GTPases Arf5 and Arl2 function partially distinctly during oocyte meiosis.

Mammalian female meiosis must be tightly regulated to produce high-quality mature oocytes for subsequent regular fertilization and healthy live birth of the next generation. GTPases control many important signal pathways involved in diverse cellular activities. ADP-ribosylation factor family members (Arfs) in mice possess GTPase activities, and some members have been found to function in meiosis. However, whether other Arfs play a role in meiosis is unknown. In this study, we found that Arl2 and Arf5 are the richest among Arfs in mouse oocytes, and they are more abundant in oocytes than in granular cells. Furthermore, Arl2 and Arf5 depletion both impeded meiotic progression, but by affecting spindles and microfilaments, respectively. Moreover, Arl2 and Arf5 depletion both significantly increased regular reactive oxygen species levels and decreased mitochondrial membrane potential and autophagy, indicating that oocyte quality was damaged by Arl2 and Arf5 depletion. These results suggest that Arl2 and Arf5 are two novel essential GTPases required for oocyte meiosis and quality control.

Specificity, promiscuity and localization of ARF protein interactions with NCS-1 and phosphatidylinositol-4 kinase-III beta.

ADP-ribosylation factor (ARF) proteins are involved in multiple intracellular vesicular transport pathways. Most studies have focused on the functions of ARF1 or ARF6 and little is known about the remaining ARF isoforms. Although the mammalian ARF proteins share a high degree of sequence identity, recent evidence has indicated that they may control distinct trafficking steps within cells. A unanswered issue is the degree of specificity of ARF family members for different interacting proteins. To investigate potential functional differences between the human ARF proteins, we have examined the localization of all human ARF isoforms and their interactions with two ARF1 binding proteins, neuronal calcium sensor-1 (NCS-1) and phosphatidylinositol-4 kinase-IIIbeta (PI4Kbeta). Use of a fluorescent protein fragment complementation method showed direct interactions between ARFs 1, 3, 5 and 6 with NCS-1 but at different intracellular locations in live HeLa cells. Photobleaching experiments indicated that complementation did not detect dynamic changes in protein interactions over short-time scales. A more specific interaction between ARFs 1/3 and PI4Kbeta was observed. Consistent with these latter findings ARF1 but not ARF5 or 6 enhanced the stimulatory effect of PI4Kbeta on regulated exocytosis, suggesting a specific role for class-I ARFs in the regulation of PI4Kbeta.

Cancer Familial Aggregation (CFA) and G446A polymorphism in ARLTS1 gene

ARLTS1--a member of ADP-ribosylation factor family, is a newly described candidate tumour suppressor gene. Recent studies show that a nonsense polymorphism, G446A (Trp149Stop), in ARLTS1 gene is significantly more frequent in familial cancer cases than in sporadic cancer cases. This study presents analysis of the germ-line G446A polymorphism in the ARLTS1 gene among 1686 consecutively collected patients with breast cancer, prostate cancer, malignant melanoma, thyroid papillary cancer or laryngeal cancer in Poland. The G446A allele was present in 1.81% (9/497) breast cancer patients, 1.46% (5/343) prostate cancer patients, 1.76% (7/397) melanoma patients, 1.65% (3/182) thyroid papillary carcinoma patients and 2.68% (8/299) of laryngeal cancer patients. The frequency of this polymorphism in the control group was 1.45% (8/552). Differences in the frequency of the G446A polymorphism between case and control groups were not statistically significant. In addition, there was no significant difference in the number of Cancer Familial Aggregations (CFA) among breast, prostate, thyroid or laryngeal cancer cases harbouring the G446A polymorphism, when compared to the G446A negative cases. Interestingly out of the CFA melanoma cases, 4/6 (66.6%) were found to harbour the change compared to only 20.2% (69/341) sporadic melanoma cases. This difference was statistically significant (p = 0.02, OR = 7.8). The results of this study suggest that the G446A in ARLTS1 gene is probably not associated with an increased risk of sporadic breast cancer, prostate cancer, melanoma, thyroid papillary cancer or laryngeal cancer. Moreover, the G446A polymorphism is not significantly more frequent in CFA cases except for families in which the proband had melanoma. To confirm this result more cases of melanoma should be analysed.

Comparative Activity of ADP-ribosylation Factor Family Members in the Early Steps of Coated Vesicle Formation on Rat Liver Golgi Membranes

We have compared the abilities of mammalian ADP-ribosylation factors (ARFs) 1, 5, and 6 and Saccharomyces cerevisiae ARF2 to serve as substrates for the rat liver Golgi membrane guanine nucleotide exchange factor and to initiate the formation of clathrin- and coatomer protein (COP) I-coated vesicles on these membranes. While Golgi membranes stimulated the exchange of GTPgammaS for GDP on all of the ARFs tested, mammalian ARF1 was the best substrate, with an apparent Km of 5 microM. In all cases myristoylation of ARF was required for stimulation. Agents that inhibit the Golgi membrane guanine nucleotide exchange factor (the fungal metabolite brefeldin A and trypsin treatment) selectively inhibited the guanine nucleotide exchange on mammalian ARF1. Taken together, these data indicate that of the ARFs tested, only mammalian ARF1 is activated efficiently by the Golgi guanine nucleotide exchange factor. The other ARFs are activated mainly by another mechanism, possibly phospholipid-mediated. Once activated, all of the membrane-associated, myristoylated ARFs promoted the recruitment of coatomer to about the same extent. Mammalian ARFs 1 and 5 were the most effective in promoting the recruitment of the AP-1 adaptor complex, whereas yeast ARF2 was the least active. These data indicate that the specificity for ARF action on the Golgi membranes is primarily determined by the Golgi guanine nucleotide exchange factor, which has a strong preference for myristoylated mammalian ARF1.