Human IgG1 antibodies suppress angiogenesis in a target-independent manner.

Aberrant angiogenesis is implicated in diseases affecting nearly 10% of the world's population. The most widely used anti-angiogenic drug is bevacizumab, a humanized IgG1 monoclonal antibody that targets human VEGFA. Although bevacizumab does not recognize mouse Vegfa, it inhibits angiogenesis in mice. Here we show bevacizumab suppressed angiogenesis in three mouse models not via Vegfa blockade but rather Fc-mediated signaling through FcγRI (CD64) and c-Cbl, impairing macrophage migration. Other approved humanized or human IgG1 antibodies without mouse targets (adalimumab, alemtuzumab, ofatumumab, omalizumab, palivizumab and tocilizumab), mouse IgG2a, and overexpression of human IgG1-Fc or mouse IgG2a-Fc, also inhibited angiogenesis in wild-type and FcγR humanized mice. This anti-angiogenic effect was abolished by Fcgr1 ablation or knockdown, Fc cleavage, IgG-Fc inhibition, disruption of Fc-FcγR interaction, or elimination of FcRγ-initated signaling. Furthermore, bevacizumab's Fc region potentiated its anti-angiogenic activity in humanized VEGFA mice. Finally, mice deficient in FcγRI exhibited increased developmental and pathological angiogenesis. These findings reveal an unexpected anti-angiogenic function for FcγRI and a potentially concerning off-target effect of hIgG1 therapies.

Cyclin-dependent kinase 5 promotes the stability of corneal epithelial cell junctions.

PURPOSE: Although cyclin-dependent kinase 5 (Cdk5) inhibits the formation of junctions containing N-cadherin, the effect of Cdk5 on junctions containing E-cadherin is less clear. The present study investigates the functional significance of Cdk5 in forming and maintaining cell-cell stability in corneal epithelial cells. METHODS: A Cdk5-deficient human corneal limbal epithelial cell line was generated by lentiviral transduction of small hairpin RNA specific for Cdk5 (shCdk5-HCLE cells). A blasticidin-inducible vector for expression of Cdk5-specific short hairpin RNA (ShCdk5) was generated by recombination and packaged into non-replicative lentiviral particles for transduction of human corneal limbal epithelial (HCLE) cells. Blasticidin-resistant cells were isolated for analysis. Cell aggregations were performed using HCLE, Cdk5 inhibitor olomoucine, ShCdk5, and MDA-MB 231 cells in the presence and absence of calcium, and particle size was measured using image analysis software. Relative protein concentrations were measured with immunoblotting and quantitative densitometry. Total internal reflection fluorescence (TIRF) microscopy was performed on cells transfected with green fluorescent protein (GFP)-E-cadherin or GFP-p120, and internalization of boundary-localized proteins was analyzed with particle tracking software. The stability of surface-exposed proteins was determined by measuring the recovery of biotin-labeled proteins with affinity chromatography. Rho and Rac activity was measured with affinity chromatography and immunoblotting. RESULTS: Examining the effect of Cdk5 on E-cadherin containing epithelial cell-cell adhesions using a corneal epithelial cell line (HCLE), we found that Cdk5 and Cdk5 (pY15) coimmunoprecipitate with E-cadherin and Cdk5 (pY15) colocalizes with E-cadherin at cell-cell junctions. Inhibiting Cdk5 activity in HCLE or suppressing Cdk5 expression in a stable HCLE-derived cell line (ShHCLE) decreased calcium-dependent cell adhesion, promoted the cytoplasmic localization of E-cadherin, and accelerated the loss of surface-biotinylated E-cadherin. TIRF microscopy of GFP-E-cadherin in transfected HCLE cells showed an actively internalized sub-population of E-cadherin, which was not bound to p120 as it was trafficked away from the cell-cell boundary. This population increased in the absence of Cdk5 activity, suggesting that Cdk5 inhibition promotes dissociation of p120/E-cadherin junctional complexes. These effects of Cdk5 inhibition or suppression were accompanied by decreased Rac activity, increased Rho activity, and enhanced binding of E-cadherin to the Rac effector Ras GTPase-activating-like protein (IQGAP1). Cdk5 inhibition also reduced adhesion in a cadherin-deficient cell line (MDA-MB-231) expressing exogenous E-cadherin, although Cdk5 inhibition promoted adhesion when these cells were transfected with N-cadherin, as previous studies of Cdk5 and N-cadherin predicted. Moreover, Cdk5 inhibition induced N-cadherin expression and formation of N-cadherin/p120 complexes in HCLE cells. CONCLUSIONS: These results indicate that loss of Cdk5 activity destabilizes junctional complexes containing E-cadherin, leading to internalization of E-cadherin and upregulation of N-cadherin. Thus, Cdk5 activity promotes stability of E-cadherin-based cell-cell junctions and inhibits the E-cadherin-to-N-cadherin switch typical of epithelial-mesenchymal transitions.

A subset of human limbal epithelial cells with greater nucleus-to-cytoplasm ratio expressing high levels of p63 possesses slow-cycling property.

PURPOSE: The purpose of this study was to evaluate the subset of limbal epithelial cells with greater nucleus-to-cytoplasm (N/C) ratio expressing high levels of p63 for their slow-cycling property, a characteristic feature of stem cells (SCs). METHODS: Limbal and peripheral corneal explant cultures were pulse labeled with 5-5-bromo-2'-deoxyuridine (BrdU) for 5 days, followed by a period of 3-week chase. Cultured explants were cryosectioned and stained for BrdU. The epithelial cells in the outgrowth and those remaining on the explant were isolated and subjected to cytospin and double immunostaining for BrdU and p63, followed by identification of label-retaining cells (LRCs) and quantification of p63 expression using confocal microscopy. RESULTS: A distinct population of small cells with large N/C ratio expressing high levels of p63 retained the BrdU label after 21-day chase. Further, this population of LRCs, negative for the differentiation marker K3, was observed in the epithelial outgrowth of limbal but not in that of peripheral cornea. LRCs were seen to migrate along the cut edge of limbal explants in culture and were also observed as clusters of small cells in the outgrowth, which contained cells with the ability to form holoclone colonies. CONCLUSIONS: These results demonstrate that the small cells with large N/C ratio and high levels of p63 have BrdU label retaining slow-cycling property, thus confirming that these 2 parameters in combination may serve as a precise marker for identification and quantification of ex vivo-expanded limbal SCs. This method would be useful to standardize the optimal culture conditions that can maintain and expand SCs for therapeutic applications.

A method to isolate human limbal basal cells enriched for a subset of epithelial cells with a large nucleus/cytoplasm ratio expressing high levels of p63.

The objectives were to develop method of isolating viable human limbal basal cells in order to enrich a subset of small cells with a large Nucleus/Cytoplasm (N/C) ratio expressing high levels of p63, nuclear protein. Limbal tissues were treated with trypsin for 50 min at 37 degrees C in an orbital shaker at 100 rpm with epithelial side down followed by additional 5 min with epithelial side up and then with Dispase II to obtain various epithelial fractions. Isolated cell fractions were assessed for colony forming efficiency and DeltaNp63alpha, connexin (Cx43) mRNA levels. Cytospin smears were double-immunostained for p63 and any one of the stem cell (SC) related markers and analyzed using a laser scanning confocal microscope and advanced image analysis software (Leica Confocal software, 2.61 build 1537 version) for quantification of fluorescence intensity. The isolated limbal basal cells were highly positive for DeltaNp63alpha mRNA but expressing low Cx43 mRNA. They gave rise to higher number of large colonies with compact morphology in contrast to the limbal suprabasal/superficial (LS/S) colonies. Furthermore, a subset with a large N/C ratio expressing high levels of p63 was observed, as much as 25% among the limbal basal cell fraction, in contrast to only about 4% in the total limbal epithelial cells. Such cells were positive for K5 and negative for Ki67, Cx43, and 14-3-3s and were absent in the LS/S fraction. These results collectively substantiate our method of isolation of limbal basal layer cells containing an enriched population of cells with SC phenotype.

High expression of p63 combined with a large N/C ratio defines a subset of human limbal epithelial cells: implications on epithelial stem cells.

PURPOSE: To characterize human limbal epithelial cells based on the expression levels of nuclear protein p63 and the nucleus-to-cytoplasm (N/C) ratio. METHODS: Limbal, peripheral, and central corneal epithelia were separated from the stroma by Dispase II and subsequently were treated with trypsin to obtain single-cell suspensions. Cytospin smears of the cell suspensions were double immunostained for p63 and then stained for any one of the markers (acidic cytokeratins [AE1], K5, K3, or connexin 43 [Cx43]). They were counterstained with propidium iodide. More than 100 cells from each zone were analyzed for p63 expression levels and nuclear/cellular area using quantitative confocal microscopy. RESULTS: A gradient of p63-positive cells was observed in corneal and limbal epithelial cells. The percentage of p63-positive cells and the level of p63 expression were significantly higher in the limbal than in the peripheral or central corneal epithelium. Two-parameter (p63 levels and N/C ratio) analysis revealed the presence of a distinct population of small cells with higher levels of p63 and a large N/C ratio in the limbal epithelium. Such limbal epithelial cells were positive for AE1 and K5 but negative for K3 and Cx43. CONCLUSIONS: These results suggest that this distinct group of small cells in the limbal epithelium with greater N/C ratio, expressing high levels of nuclear protein p63, probably represent corneal epithelial stem cells.