Relationships between Rap1b, Affinity Modulation of Integrin α IIb β 3 , and the Actin Cytoskeleton

The affinity of integrin alpha(IIb)beta(3) for fibrinogen is controlled by inside-out signals that are triggered by agonists like thrombin. Agonist treatment of platelets also activates Rap1b, a small GTPase known to promote integrin-dependent adhesion of other cells. Therefore, we investigated the role of Rap1b in alpha(IIb)beta(3) function by viral transduction of GFP-Rap1 chimeras into murine megakaryocytes, which exhibit inside-out signaling similar to platelets. Expression of constitutively active GFP-Rap1b (V12) had no effect on unstimulated megakaryocytes, but it greatly augmented fibrinogen binding to alpha(IIb)beta(3) induced by a PAR4 thrombin receptor agonist (p < 0.01). The Rap1b effect was cell-autonomous and was prevented by pre-treating cells with cytochalasin D or latrunculin A to inhibit actin polymerization. Rap1b-dependent fibrinogen binding to megakaryocytes was blocked by POW-2, a novel monovalent antibody Fab fragment specific for high affinity murine alpha(IIb)beta(3). In contrast to GFP-Rap1b (V12), expression of GFP-Rap1GAP, which deactivates endogenous Rap1, inhibited agonist-induced fibrinogen binding (p < 0.01), as did dominant-negative GFP-Rap1b (N17) (p < 0.05). None of these treatments affected surface expression of alpha(IIb)beta(3). These studies establish that Rap1b can augment agonist-induced ligand binding to alpha(IIb)beta(3) through effects on integrin affinity, possibly by modulating alpha(IIb)beta(3) interactions with the actin cytoskeleton

Phenotypic Plasticity of Mouse Spermatogonial Stem Cells

BACKGROUND:Spermatogonial stem cells (SSCs) continuously undergo self-renewal division to support spermatogenesis. SSCs are thought to have a fixed phenotype, and development of a germ cell transplantation technique facilitated their characterization and prospective isolation in a deterministic manner; however, our in vitro SSC culture experiments indicated heterogeneity of cultured cells and suggested that they might not follow deterministic fate commitment in vitro. METHODOLOGY AND PRINCIPAL FINDINGS:In this study, we report phenotypic plasticity of SSCs. Although c-kit tyrosine kinase receptor (Kit) is not expressed in SSCs in vivo, it was upregulated when SSCs were cultured on laminin in vitro. Both Kit(-) and Kit(+) cells in culture showed comparable levels of SSC activity after germ cell transplantation. Unlike differentiating spermatogonia that depend on Kit for survival and proliferation, Kit expressed on SSCs did not play any role in SSC self-renewal. Moreover, Kit expression on SSCs changed dynamically once proliferation began after germ cell transplantation in vivo. CONCLUSIONS/SIGNIFICANCE:These results indicate that SSCs can change their phenotype according to their microenvironment and stochastically express Kit. Our results also suggest that activated and non-activated SSCs show distinct phenotypes

The integrin-linked kinase-PINCH-parvin complex supports integrin αIIbβ3 activation.

Integrin-linked kinase (ILK) is an important signaling regulator that assembles into the heteroternary complex with adaptor proteins PINCH and parvin (termed the IPP complex). We recently reported that ILK is important for integrin activation in a Chinese hamster ovary (CHO) cell system. We previously established parental CHO cells expressing a constitutively active chimeric integrin (αIIbα6Bβ3) and mutant CHO cells expressing inactive αIIbα6Bβ3 due to ILK deficiency. In this study, we further investigated the underlying mechanisms for ILK-dependent integrin activation. ILK-deficient mutant cells had trace levels of PINCH and α-parvin, and transfection of ILK cDNA into the mutant cells increased not only ILK but also PINCH and α-parvin, resulting in the restoration of αIIbα6Bβ3 activation. In the parental cells expressing active αIIbα6Bβ3, ILK, PINCH, and α-parvin were co-immunoprecipitated, indicating the formation of the IPP complex. Moreover, short interfering RNA (siRNA) experiments targeting PINCH-1 or both α- and β-parvin mRNA in the parent cells impaired the αIIbα6Bβ3 activation as well as the expression of the other components of the IPP complex. In addition, ILK mutants possessing defects in either PINCH or parvin binding failed to restore αIIbα6Bβ3 activation in the mutant cells. Kindlin-2 siRNA in the parental cells impaired αIIbα6Bβ3 activation without disturbing the expression of ILK. For CHO cells stably expressing wild-type αIIbβ3 that is an inactive form, overexpression of a talin head domain (THD) induced αIIbβ3 activation and the THD-induced αIIbβ3 activation was impaired by ILK siRNA through a significant reduction in the expression of the IPP complex. In contrast, overexpression of all IPP components in the αIIbβ3-expressing CHO cells further augmented THD-induced αIIbβ3 activation, whereas they did not induce αIIbβ3 activation without THD. These data suggest that the IPP complex rather than ILK plays an important role and supports integrin activation probably through stabilization of the active conformation

Characterization of ILK-deficient mutant cells expressing inactive αIIbα6Bβ3.

<p>(A) Immunoblotting for ILK, PINCH, α-parvin, talin, and kindlin-2. Cell lysates obtained from parental cells with constitutively active αIIbα6Bβ3, ILK-deficient mutant cells with inactive αIIbα6Bβ3, and mutant cells transiently transfected with rat ILK cDNA were electrophoresed on SDS-PAGE gels and immunoblotted with indicated Abs. GAPDH shows an internal loading control. (B) Flow cytometry analysis showing PAC-1 (an activation-specific mAb for αIIbβ3) binding to mutant cells transiently transfected with either ILK plasmid or empty plasmid. Bound PAC-1 was detected with a PE-conjugated secondary mAb. </p

Detection of IPP complex proteins in αIIbα6Bβ3-active parental cells.

<p>Cell lysates obtained from αIIbα6Bβ3-active parental cells were immunoprecipitated with Abs against PINCH (A), α-parvin (B, C), and ILK (D). The co-precipitates were detected by Abs for α-parvin (A), ILK (B), and PINCH (C, D). IgG means immunoprecipitation (IP) using non-immune control IgG. IB stands for immunoblotting. Arrows indicate the predicted sizes of the indicated proteins. Arrowheads (D) indicate the antibody heavy chains used in the IP. Different mobilities between those of the two IgG antibodies are probably caused by differences in the amino acid compositions of them. </p

Knockdown effects of PINCH, parvins, and kindlin-2 in αIIbα6Bβ3-active parental cells.

<p>αIIbα6Bβ3-active parental cells were transiently transfected with PINCH siRNAs (p157 and p755) (A), α-parvin siRNAs (pa503 and pa761) (C), β-parvin siRNAs (pb900 and pb1011) (C), kindlin-2 siRNAs (k770 and k1733) (E), negative control siRNAs, and scrambled siRNAs. Cell lysates were electrophoresed on SDS-PAGE gels, and the separated proteins were immunoblotted with the indicated Abs. GAPDH and β-actin are shown as internal loading controls. The activation indexes of transfected cells (B, D, F) were calculated using the formula shown in Materials and Methods. A value of 100% implies the maximum PAC-1 binding to the cells treated with dithiothreitol (DTT). Data represent means ± standard deviation (SD) of three (B, F) or four (D) independent experiments. ** indicates <i>P</i> < 0.01.</p

Effects of ILK mutants with defects in either PINCH or parvin binding.

<p>The activation indexes of transfected cells (A, C, E). ILK-deficient mutant cells were transiently transfected with GFP cDNA, GFP-fused wild-type ILK (GFPILK-WT) cDNA, GFP-fused ILK mutant with defective PINCH binding (GFPILK-H99D/F109A/W110A) cDNA (A, E), or GFP-fused ILK mutant with defective parvin binding (GFPILK-M402A/K403A) cDNA (C, E). After transfection, the binding of either PAC-1 (A, C) or fibrinogen (E) to the cells was analyzed by flow cytometry. The activation index was determined by the formula shown in Materials and Methods. A value of 100% represents the maximal binding of PAC-1 or fibrinogen to the cells treated with dithiothreitol. Data represent means ± SD of three independent experiments. ** indicates <i>P</i> < 0.01. Immunoblotting showing protein expression of GFP (B, D), GFP-fused wild-type ILK (GFPILK-WT) (B, D), GFP-fused ILK mutant with defective PINCH binding (GFPILK-H99D/F109A/W110A) (B), and GFP-fused ILK mutant with defective parvin binding (GFPILK-M402A/K403A) (D) in ILK-deficient mutant cells. Cell lysates were electrophoresed and immunoblotted with indicated Abs. </p

Direct comparison of 3 PCR methods in detecting EGFR mutations in patients with advanced non-small-cell lung cancer

Epidermal growth factor receptor (EGFR) mutations are predictive of response to EGFR tyrosine kinase inhibitors (TKIs) in NSCLC. Several methods have been used to detect EGFR mutations; however, it is not clear which is the most suitable for use in the clinic. In this study, we directly compare the clinical sensitivity and specificity of 3 PCR methods. We compared the 3 PCR methods (mutant-enriched PCR, PNA-LNA PCR, and PCR clamp) in patients with advanced NSCLC. A patient who showed sensitive mutations by at least 1 PCR method was treated with gefitinib. A patient who showed no sensitive mutations was treated with chemotherapy with cytotoxic agents. Fifty patients with advanced NSCLC previously untreated with EGFR-TKIs were enrolled in this trial. Seventeen patients were harboring EGFR mutations, 5 of whom showed discrepancies between the results of different PCR methods. All 5 patients responded to gefitinib. All patients harboring EGFR mutations received gefitinib treatment and 21 of 33 EGFR-mutation-negative patients received chemotherapy with cytotoxic agents. Median progression-free survival of the gefitinib group and the chemotherapy group were 8.2 and 5.9 months, respectively. We considered that all the discrepancies might be false negatives because the patients responded to gefitinib. To clarify the reason for the false negatives of each PCR method, and establish the clinical sensitivity and specificity of each PCR method, a large prospective clinical trial is warranted