Epidermal growth factor stimulates extracellular-signal regulated kinase phosphorylation of a novel site on cytoplasmic Dynein intermediate chain 2

km23-1/DYNLRB1 regulation of MEK/ERK signaling and R-Ras in invasive human colorectal cancer cells

We previously found that km23-1/DYNLRB1 is required for transforming growth factor-β (TGFβ) production through Ras/ERK pathways in TGFβ-sensitive epithelial cells and in human colorectal cancer (CRC) cells. Here we demonstrate that km23-1/DYNLRB1 is required for mitogen-activated protein kinase kinase (MEK) activation in human CRC cells, detected by km23-1/DYNLRB1-siRNA inhibition of phospho-(p)-MEK immunostaining in RKO cells. Furthermore, we show that CRISPR-Cas9 knock-out (KO) of km23-1/DYNLRB1 reduced cell migration in two additional CRC models, HCT116 and DLD-1. Of interest, in contrast to our previous work showing that dynein motor activity was required for TGFβ-mediated nuclear translocation of Smad2, in the current report, we demonstrate for the first time that disruption of dynein motor activity did not reduce TGFβ-mediated activation of MEK1/2 or c-Jun N-terminal kinase (JNK). Moreover, size exclusion chromatography of RKO cell lysates revealed that B-Raf, extracellular signal-regulated kinase (ERK), and p-ERK were not present in the large molecular weight fractions containing dynein holocomplex components. Furthermore, sucrose gradient fractionation of cell lysates from both HCT116 and CBS CRC cells demonstrated that km23-1/DYNLRB1 co-sedimented with Ras, p-ERK, and ERK in fractions that did not contain components of holo-dynein. Thus, km23-1/DYNLRB1 may be associated with activated Ras/ERK signaling complexes in cell compartments that do not contain the dynein holoprotein complex, suggesting dynein-independent km23-1/DYNLRB1 functions in Ras/ERK signaling. Finally, of the Ras isoforms, R-Ras is most often associated with cell migration, adhesion, and protrusive activity. Here, we show that a significant fraction of km23-1/DYNLRB1 and RRas wase co-localized at the protruding edges of migrating HCT116 cells, suggesting an important role for the km23-1/DYNLRB1-R-Ras complex in CRC invasion.

Inositol hexakisphosphate kinase 1 (IP6K1) activity is required for cytoplasmic dynein-driven transport

Inositol pyrophosphates, such as diphosphoinositol pentakisphosphate (IP7), are conserved eukaryotic signaling molecules that possess pyrophosphate and monophosphate moieties. Generated predominantly by inositol hexakisphosphate kinases (IP6Ks), inositol pyrophosphates can modulate protein function by posttranslational serine pyrophosphorylation. Here, we report inositol pyrophosphates as novel regulators of cytoplasmic dynein-driven vesicle transport. Mammalian cells lacking IP6K1 display defects in dynein-dependent trafficking pathways, including endosomal sorting, vesicle movement, and Golgi maintenance. Expression of catalytically active but not inactive IP6K1 reverses these defects, suggesting a role for inositol pyrophosphates in these processes. Endosomes derived from slime mold lacking inositol pyrophosphates also display reduced dynein-directed microtubule transport. We demonstrate that Ser51 in the dynein intermediate chain (IC) is a target for pyrophosphorylation by IP7, and this modification promotes the interaction of the IC N-terminus with the p150(Glued) subunit of dynactin. IC-p150(Glued) interaction is decreased, and IC recruitment to membranes is reduced in cells lacking IP6K1. Our study provides the first evidence for the involvement of IP6Ks in dynein function and proposes that inositol pyrophosphate-mediated pyrophosphorylation may act as a regulatory signal to enhance dynein-driven transport.

Recent advances and challenges in plant phosphoproteomics

Plants are sessile organisms that need to respond to environmental changes quickly and efficiently. They can accomplish this by triggering specialized signaling pathways often mediated by protein phosphorylation and dephosphorylation. Phosphorylation is a fast response that can switch on or off a myriad of biological pathways and processes. Proteomics and MS are the main tools employed in the study of protein phosphorylation. Advances in the technologies allow simultaneous identification and quantification of thousands of phosphopeptides and proteins that are essential to understanding the sophisticated biological systems and regulations. In this review, we summarize the advances in phosphopeptide enrichment and quantitation, MS for phosphorylation site mapping and new data acquisition methods, databases and informatics, interpretation of biological insights and crosstalk with other PTMs, as well as future directions and challenges in the field of phosphoproteomics.

Distinct functional roles of cytoplasmic dynein defined by the intermediate chain isoforms

The motor protein, cytoplasmic dynein is responsible for the movement of a variety of cargoes toward microtubule minus ends in cells. Little is understood about how dynein is regulated to specifically transport its various cargoes. In vertebrates, the dynein motor domain (DYNC1H) is encoded by a single gene; while there are two genes for the five smaller subunits that comprise the cargo binding domain of the dynein complex. The isoforms of the intermediate chain (DYNC1I) provide a good model system with which to study the roles the different isoforms of the cargo domain subunits have in designating specific dynein functions. The intermediate chains (DYNC1I) play a key scaffold role in the dynein complex. In neurons, dynein complexes with different intermediate chain isoforms have distinct roles, including cargo binding and transport. Some of the phospho-isoforms of the intermediate chain also specify binding to specific cargo. These data support the model that cytoplasmic dynein can be specifically regulated through the different isoforms of the subunits.

Editorial of the special issue: signaling molecules and signal transduction in cells

In the special issue “Signaling Molecules and Signal Transduction in Cells” authors were invited to submit papers regarding important and novel aspects of extra- and intracellular signaling which have implications on physiological and pathophysiological processes. These aspects included compounds which are involved in these processes, elucidation of signaling pathways, as well as novel techniques for the analysis of signaling pathways. In response, various novel and important topics are elucidated in this special issue.