Biology subjects

Rajapakse, N.

Publications and source records attributed to Rajapakse, N..

5 recordsLinked to original sources

bioRxiv2022

Men in menopause? Experimental verification of the mate choice theory of menopause with Drosophila melanogaster

Various hypotheses regarding the origin of menopause have been proposed, and although the kin-selection-based theory appears promising, it involves population genetic processes that are insufficient to compensate for loss of fitness. The grandmother hypothesis and its variation the live long hypothesis are untenable; the former requires "climbing a steep fitness hill", as grandmothers share only 25% of their genes with their grandchildren, compared to 50% with their direct offspring, while the latter proposes a prolongation of the post-menopausal lifespan through selection, which is impossible in a population of non-reproducing females. The mate choice theory explains menopause as the result of asymmetric mating involving younger females and older males that leads to an accumulation of infertility mutations and the evolution of menopause in older females. In this study, we investigated the mate choice theory using an infertility mutation accumulation experiment with Drosophila melanogaster that involved mating between individuals of different age groups. After 70 generations of asymmetric mating, the results showed that younger females who were paired with older males showed declining fertility in old age. The same trend was noted with younger males when mated with older females; the fertility of the males declined in old age. These results support the mate choice theory and indicate that menopause is not a life history trait of females but of the sex of the younger mate. Mate choice theory treats the evolution of menopause and post-menopausal lifespan as independent traits that are driven by the mate choices exercised by older males. Menopause may be an atypical process because the evolutionary mechanism (age-restricted asymmetric mating) involved is rarely observed.

evolutionary biology↗

bioRxiv2021

GIV/Girdin binds BRCA1 and links trimeric G-proteins to DNA damage response

Upon sensing DNA double-strand breaks (DSBs), eukaryotic cells either die or repair DSBs via one of two competing pathways, i.e., non-homologous end-joining (NHEJ) or homologous recombination (HR). We show that cell fate after DNA damage hinges on the guanine nucleotide-exchange modulator of heterotrimeric G-protein, Gi*{beta}{gamma}, GIV/Girdin. GIV suppresses HR by binding and sequestering BRCA1, a key coordinator of multiple steps within the HR pathway, away from DSBs; it does so using a C-terminal motif that binds BRCA1s BRCT-modules via both phospho-dependent and -independent mechanisms. GIV promotes NHEJ, and binds and activates Gi and enhances the free G{beta}{gamma}[->]PI-3-kinase[->]Akt pathway, thus revealing the enigmatic origin of prosurvival Akt signals during dsDNA repair. Absence of GIV, or the loss of either of its two functions impaired DNA repair, and induced cell death when challenged with numerous cytotoxic agents. That GIV selectively binds few other BRCT-containing proteins suggests convergent signaling such that heterotrimeric G-proteins may finetune sensing, repair, and outcome after DNA damage. GRAPHIC ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=190 SRC="FIGDIR/small/452842v3_ufig1.gif" ALT="Figure 1"> View larger version (66K): org.highwire.dtl.DTLVardef@3d5202org.highwire.dtl.DTLVardef@1d32d89org.highwire.dtl.DTLVardef@152a85dorg.highwire.dtl.DTLVardef@1ab9953_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LINon-receptor G protein modulator, GIV/Girdin binds BRCA1 C_LIO_LIBinding occurs in both canonical and non-canonical modes C_LIO_LIGIV sequesters BRCA1 away from dsDNA breaks, suppresses HR C_LIO_LIActivation of Gi by GIV enhances Akt signals, favors NHEJ C_LI IN BRIEFIn this work, the authors show that heterotrimeric G protein signaling that is triggered by non-receptor GEF, GIV/Girdin, in response to double-stranded DNA breaks is critical for decisive signaling events which favor non-homologous end-joining (NHEJ) and inhibit homologous recombination (HR).

cancer biology↗

bioRxiv2020

Evolution of Modularity, Interactome and Functions of GIV/Girdin (CCDC88A) from Invertebrates to Vertebrates

PDZ domains are one of the most abundant protein domains in eukaryotes and frequently found on junction-localized scaffold proteins. Various signaling molecules bind to PDZ proteins via PDZ-binding motifs (PBM) and finetune cellular signaling. Here we describe the presence of a PBM on GIV/Girdin (CCDC88A) that is conserved throughout evolution, from invertebrates to vertebrates, and is generated as a long isoform-variant in humans, which we named GIV-L. Unlike GIV, which lacks PBM and is cytosolic, GIV-L localizes to the cell junctions, and has a unique PDZ-interactome, which impacts GIV-Ls ability to bind and activate trimeric G-protein, Gi through its guanine-nucleotide exchange modulator (GEM) module; the GEM module is found exclusively in vertebrates. Thus, the two functional modules in GIV evolved sequentially: the ability to bind PDZ proteins via the PBM evolved earlier in invertebrates, whereas G-protein binding and activation may have evolved later only among vertebrates. Phenotypic studies in Caco-2 cells revealed that GIV and GIV-L may have antagonistic effects on cell growth, proliferation (cell cycle), and survival. Immunohistochemical analyses in human colon tissues showed that GIV expression increases with a concomitant decrease in GIV-L during cancer initiation. Taken together, these findings reveal how GIV/CCDC88A in humans displays evolutionary flexibility in modularity, which allows the resultant isoforms to play opposing roles either as a tumor suppressor (GIV-L) or as an oncogene (GIV).

biochemistry↗

bioRxiv2019

GIV-Kindlin interaction is required for Kindlin-Mediated Integrin Recognition and Activation

Cells perceive and respond to the extracellular matrix (ECM) via integrin receptors; their dysregulation has been implicated in inflammation and cancer metastasis. Here we show that a guanine nucleotide exchange modulator of trimeric-GTPase Gi, GIV (a.k.a Girdin), directly binds the integrin adaptor Kindlin-2. A non-canonical short linear motif within GIVs C-terminus binds Kindlin-2-FERM3 domain at a site that is distinct from the binding site for the canonical NPxY motif on the -integrin tail. Binding of GIV to Kindlin-2 allosterically enhances Kindlin-2s affinity for {beta}1-integrin. Consequently, integrin activation and clustering are maximized, which augments cell adhesion, spreading and invasion. Findings elucidate how the GIV*Kindlin-2 complex has a two-fold impact: it allosterically synergizes integrin activation and enables {beta}1-integrins to indirectly access and modulate trimeric GTPases via the complex. Furthermore, Cox proportional-hazard models on tumor transcriptomics provide trans-scale evidence of synergistic interactions between GIV*Kindlin-2*{beta}1-integrin on time to progression to metastasis. The eTOC blurbIntegrins mediate cell adhesion to the extracellular matrix; their dysregulation fuels inflammation, cancer cell invasion and metastasis. Authors show how two pro-metastatic scaffold proteins, Kindlin and GIV/Girdin bind and cooperatively enhance their allosteric coupling to integrins, and their subsequent activation. Findings reveal novel interfaces in integrin signaling for pharmacologic manipulation. HIGHLIGHTSO_LIGIV and Kindlin(K2), two integrin adaptors that promote metastasis, bind each other C_LIO_LIBinding of GIV or integrin to K2 allosterically enhances GIV*K2*integrin complexes C_LIO_LIBinding is required for the maximal recruitment of GIV and K2 to active integrins C_LIO_LIBinding facilitates integrin clustering, activation, tumor cell adhesion, invasion. C_LI

cell biology↗

bioRxiv2019

GIV/Girdin and Exo70 Constitute the Core of the Mammalian Polarized Exocytic Machinery

Polarized exocytosis is a fundamental process by which membrane and cargo proteins are delivered to the plasma membrane with precise spatial control; it is essential for cell growth, morphogenesis, and migration. Although the need for the octameric exocyst complex is conserved from yeast to humans, what imparts spatial control is known only in yeast, i.e., a polarity scaffold without mammalian homolog, called Bem1p. We demonstrate that polarity scaffold GIV/Girdin fulfills the key criteria and functions of its yeast counterpart Bem1p. Both Bem1p and GIV bind yeast and mammalian Exo70 proteins via similar short-linear interaction motifs, but each preferentially binds its evolutionary counterpart. In cells where this GIV*Exo-70 interaction is selectively disrupted, delivery of the metalloprotease MT1-MMP to podosomes, collagen degradation and haptotaxis through basement membrane matrix were impaired. GIVs interacting partners reveal other components of polarized exocytosis in mammals. Findings not only expose how GIV "upgrades" the exocytic process in mammals, but also how the ability to regulate exocytosis shapes GIVs ability to fuel metastasis. GRAPHIC ABSTRACT O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY Graphic Abstract: Schematic comparing the components of polarized exocytosis, i.e., the major polarity scaffold in yeast (Bem1p; left) and humans (Girdin; right) and the various cellular components and signaling mechanisms that are known to converge on them. C_FIG_DISPLAY The eTOC blurbPolarized exocytosis is a precision-controlled process that is enhanced in disease states, e.g., cancer invasion; what imparts polarity was unknown. Authors reveal how the process underwent an evolutionary upgrade from yeast to humans by pinpointing GIV/Girdin as the polarity scaffold which orchestrates the exocytosis of matrix metalloproteases during cell invasion. HIGHLIGHTSO_LIGIV (human) and Bem1p (yeast) bind Exo70; are required for exocytosis C_LIO_LIGIV binds and aids PM localization Exo70 via a conserved short linear motif C_LIO_LIBinding facilitates MT1-MMP delivery to podosomes, ECM degradation, invasion C_LIO_LIRegulatory control over polarized exocytosis is upgraded during evolution C_LI

cell biology↗