Browsing by Author "Noll, Bettina"

Now showing 1 - 3 of 3

Open Access
Golgi screen identifies the RhoGEF Solo as a novel regulator of RhoB and endocytic transport
(2023) Lungu, Cristiana; Meyer, Florian; Hörning, Marcel; Steudle, Jasmin; Braun, Anja; Noll, Bettina; Benz, David; Fränkle, Felix; Schmid, Simone; Eisler, Stephan A.; Olayioye, Monilola A.
The control of intracellular membrane trafficking by Rho GTPases is central to cellular homeostasis. How specific guanine nucleotide exchange factors and GTPase‐activating proteins locally balance GTPase activation in this process is nevertheless largely unclear. By performing a microscopy‐based RNAi screen, we here identify the RhoGEF protein Solo as a functional counterplayer of DLC3, a RhoGAP protein with established roles in membrane trafficking. Biochemical, imaging and optogenetics assays further uncover Solo as a novel regulator of endosomal RhoB. Remarkably, we find that Solo and DLC3 control not only the activity, but also total protein levels of RhoB in an antagonistic manner. Together, the results of our study uncover the first functionally connected RhoGAP‐RhoGEF pair at endomembranes, placing Solo and DLC3 at the core of endocytic trafficking.
Open Access
Isoform specific functions of protein kinase D3 (PKD3) in breast cancer cell proliferation and motility
(2014) Noll, Bettina; Olayioye, Monilola (Prof. Dr.)
The protein kinase D (PKD) family of serine/threonine kinases belongs to the family of calcium/calmodulin-dependent protein (CAM) kinases and comprises three family members, PKD1, PKD2 and PKD3. By the phosphorylation of numerous protein substrates, PKDs regulate a variety of different cellular functions such as proliferation and differentiation, membrane and vesicle transport, apoptosis, gene expression, adhesion, motility and invasion. Most studies on PKDs have focused on the cellular regulation and functions of PKD1 and PKD2 and in general, the three PKD isoforms are thought to possess overlapping substrate specificities and function, at least in part, redundantly. However, emerging evidence suggests that isoform specific differences exist. Due to its structural characteristics PKD3 appears to play a unique role among the three isoforms, nevertheless it still is the least studied family member. The aim of this study was therefore to reveal isoform specific functions of PKD3 in the context of breast cancer biology. In the first part of this thesis, the regulation of cell adhesion and motility by PKD3-mediated phosphorylation of the G-protein coupled receptor kinase-interacting protein 1 (GIT1) was investigated. The continuous assembly and disassembly of focal adhesions (FA) is required for efficient cell spreading and migration. GIT1 is a multidomain protein whose dynamic localization to sites of cytoskeletal remodeling is critically involved in the regulation of these processes. Mass spectrometry analysis identified a novel phosphorylation site within GIT1 at serine 46, the phosphorylation of which was abrogated by PKD3, but not PKD1 and/or PKD2 depletion, thereby identifying GIT1 as the first PKD3-specific substrate. Functional experiments further provide support that PKD3-mediated GIT1 phosphorylation on serine 46 represents a molecular switch by which GIT1 localization and thus paxillin trafficking, cellular protrusive activity and motility of breast cancer cells are regulated. In the second part of this thesis the consequences of elevated expression of PKD3 in triple-negative breast cancer (TNBC) cells were investigated. Using a phospho-kinase signaling array, PKD3 was identified to trigger the activation of S6 kinase 1 (S6K1), a main downstream target of the mammalian target of rapamycin (mTOR) signaling pathway. Accordingly, PKD3 knockdown in TNBC cells led to reduced S6K1 phosphorylation, which was associated with impaired activation of mTOR at lysosomal membranes and the accumulation of the autophagy marker LC3. PKD3 depletion strongly inhibited proliferation of TNBC cells, most likely in part through the suppression of mTOR activation. These findings uncover a novel role for PKD3 in the homeostasis of the endolysosomal system and implicate this kinase as a potential molecular therapeutic target in TNBC. In summary, the experimental studies performed in this thesis provide novel insights into isoform specific functions of PKD3 in the context of breast cancer cell motility and the progression of TNBC.
Open Access
Spatiotemporal control of intracellular membrane trafficking by Rho GTPases
(2019) Olayioye, Monilola A.; Noll, Bettina; Hausser, Angelika
As membrane-associated master regulators of cytoskeletal remodeling, Rho GTPases coordinate a wide range of biological processes such as cell adhesion, motility, and polarity. In the last years, Rho GTPases have also been recognized to control intracellular membrane sorting and trafficking steps directly; however, how Rho GTPase signaling is regulated at endomembranes is still poorly understood. In this review, we will specifically address the local Rho GTPase pools coordinating intracellular membrane trafficking with a focus on the endo- and exocytic pathways. We will further highlight the spatiotemporal molecular regulation of Rho signaling at endomembrane sites through Rho regulatory proteins, the GEFs and GAPs. Finally, we will discuss the contribution of dysregulated Rho signaling emanating from endomembranes to the development and progression of cancer.