Abstract 1253: Fer is required for mammary tumorigenesis

Fer is a ubiquitously expressed cytoplasmic protein-tyrosine kinase (PTK) which is inducibly activated upon engagement of the epidermal and platelet-derived growth factor receptors (EGFR/PDGFR). Fer - and its homologous family member Fps/Fes - are structurally distinguished from other PTKs by a membrane-binding F-BAR domain implicated in regulating membrane-cytoskeletal dynamics during receptor endocytosis. We are investigating the role of Fer in EGFR internalization using both non-transformed mammary epithelial cells (MCF10A) and mammary tumor epithelial cells (MTEC) isolated from an ErbB2 mouse model of breast cancer. MCF10A Fer-knockdown cells (MCF10A-F2) and MTECs harboring a kinase-inactivating knock-in mutation at the fer locus (ferDR/DR) displayed elevated rates of EGF-induced endocytosis suggesting that Fer inhibits EGFR internalization. Elevated endocytic rates correlated with enhanced short-term MAPK signaling in both cell culture models and elevated steady-state Erk activity in ferDR/DR ErbB2 mammary tumors. Systems-level analyses using a physiochemical model of EGFR-MAPK signaling suggested that up-regulation of receptor endocytic rates could potentiate MAPK signal strength and sensitize this pathway to pharmacological inhibition at the receptor level. Inhibition of MAPK signaling with the EGFR/ErbB2 inhibitor, Lapatinib, confirmed this prediction, showing increased Erk signal-sensitivity to this drug in endocytosis-enhanced ferDR/DR MTECs. This correlated with a 10-fold reduction in the EC50 for Lapatinib cytotoxicity on ferDR/DR MTECs. Both the signaling and cytotoxicity phenoytypes were reversible by rescued expression of wild type Fer in ferDR/DR MTECs. These data reveal a novel mechanism by which potentiation of EGFR endocytosis enhances the sensitivity of downstream signaling to inhibition by ErbB inhibitors. In this respect, Fer is a unique kinase target because it provides a direct means of pharmacologically intervening with the mechanism of EGFR endocytosis. The therapeutic significance of potentiating receptor endocytosis by targeting Fer is highlighted by observations of: (1) delayed onset of ErbB2-mediated breast tumorigenesis in ferDR/DR genetic backgrounds in vivo; and; (2) impaired tumor growth of Fer-deficient MDA-MB-231 cells in mammary-fat pad transplantation models. We envisage that anti-Fer based treatments may sensitize breast - and potentially other carcinoma types - to anti-ErbB therapies. These observations provide biological proof-in-principle for developing small molecule inhibitor-based therapies against Fer in breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1253. doi:1538-7445.AM2012-1253

Abstract 1166: PTEN loss and ERG over-expression as prognostic biomarkers in prostate cancer and identification of downstream biomarkers with potential therapeutic value

Genomic deletion of the PTEN tumor suppressor gene and formation of the TMPRSS2:ERG gene fusion are the two most recurrent genomic aberrations in prostate cancer. The lipid phosphatase activity of PTEN negatively regulates the PI3Kinase-AKT signaling pathway, which controls numerous downstream targets such as cell cycle checkpoints, DNA damage repair with maintenance of chromosomal stability and integrity. ERG is a member of the ETS transcription factor family, whose members are implicated in numerous cellular processes including membrane remodelling, angiogenesis, differentiation, proliferation, and tumourigenesis. Emerging evidence suggests that formation of the fusion gene may promote prostatic tumourigenesis, progression, and invasive disease by elevating motility and invasiveness. The simultaneous manifestation of both PTEN loss and TMPRSS2:ERG fusion is associated with poor prognosis. This study is addressing pathways downstream of PTEN and effectors of ERG over-expression to identify additional biomarkers of prognostic and therapeutic potential. In silico genomic copy number analyses demonstrated that patient samples harboring a genomic deletion of PTEN have a greater number of genomic aberrations, in keeping with the model that loss of PTEN leads to heightened genomic instability. Mining of publically available gene expression datasets have been performed to further examine signalling pathway aberrations specific to each rearrangement. PTEN loss and ERG over-expression are being modeled in the histologically normal prostate epithelial cell line RWPE-1 using shRNA knockdown or transgene directed ectopic over-expression, respectively. Biochemical, proliferation, migration and invasion assays will be performed to determine if knockdown of PTEN leads to the expected AKT activation and increased proliferation; whereas over-expression of ERG in RWPE-1 cells correlates with heightened motility and invasive potential. Gene expression microarray profiling will also be carried out for each derivative RWPE-1 cell line using the Agilent SurePrint G3 Human Exon microarrays. This cell model system will be used to validate transcriptional changes associated with PTEN loss and ERG over-expression in prostate cancer gene expression datasets and identify potential novel downstream therapeutic targets and predictive biomarkers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1166. doi:1538-7445.AM2012-1166

Calpain 2 regulates Akt-FoxO-p27(Kip1) protein signaling pathway in mammary carcinoma

We investigated the role of the ubiquitously expressed calpain 2 isoform in breast tumor cell growth, migration, signaling, and tumorigenesis. RNAi-mediated knockdown of the capn2 transcript was used to manipulate expression of the catalytic subunit of calpain 2 in the AC2M2 mouse mammary carcinoma cell line. Stable knockdown of capn2 correlated with reduced in vitro proliferation rates, soft agar colony formation efficiency, and migration rates, indicating roles for calpain 2 in mitogenesis, survival, and motogenesis. Biochemical analysis showed increased levels of protein phosphatase 2A and reduced levels of activated Akt in calpain 2-deficient cells, and this correlated with increased levels of the FoxO3a target gene product p27(Kip1), a key regulator of cell proliferation. Calpain 2 deficiency in the AC2M2 cells correlated with enhanced nuclear localization of FoxO3a, consistent with it being in a derepressed state capable of regulating transcriptional targets. Orthotopically engrafted calpain 2 knockdown AC2M2 cells generated tumors with reduced growth rates and enhanced in vivo expression of p27(Kip1). In summary, calpain 2 deficiency correlated with reduced Akt activity, increased protein phosphatase 2A levels, derepression of FoxO3a, and enhanced expression of the p27(Kip1) tumor suppressor. These observations argue that calpain 2 promotes tumor cell growth both in vitro and in vivo through the PI3K-Akt-FoxO-p27(Kip1) signaling cascade. Inhibition of calpain 2 might therefore provide therapeutic benefits in the treatment of cancer.

Pathological significance and predictive value for biochemical recurrence of c-Fes expression in prostate cancer

BACKGROUND

c-Fes is a proto-oncogene encoded non-receptor protein-tyrosine kinase (PTK). However, genetic studies have indicated that it has anti-tumorigenic effects in certain cancers. The pathological and clinical significance of c-Fes in prostate cancer are unknown.

METHODS

Expression of c-Fes was evaluated in normal glands, prostatic intraepithelial neoplasia (PIN), cancer cells in tissues of knock-in mouse adenocarcinoma prostate (KIMAP) model, and prostate cancer patients free of metastasis. Expression of c-Fes was analyzed by immunohistochemistry, and quantified by using the immunoreactivity score (IRS) (staining intensity × percentage of positive cells). Relationships between c-Fes expression and pT stage, Gleason's score (GS), and biochemical recurrence in patients who underwent radical surgery were also investigated.

RESULTS

In KIMAP, the percentage in normal glands, PIN and cancer cells positive for c-Fes expression were 0 (0/7), 25.0 (2/8), and 100% (7/7), respectively. In human tissues, c-Fes expression was also significantly higher in cancer cells than in normal cells and PIN, and it correlated with pT stage (P < 0.001) and GS (P = 0.047). Multivariate analysis showed that c-Fes expression was an independent predictor of poor outcome poor prognosis (hazard ratio = 3.21, 95% confidence interval = 1.11-9.37, P = 0.032).

CONCLUSION

The results suggested that c-Fes expression is a useful predictor of biochemical recurrence after radical surgery. The results also suggested that c-Fes is a potentially useful therapeutic target in prostate cancer and a predictor of biochemical recurrence after radical prostatectomy.

The contrasting oncogenic and tumor suppressor roles of FES

The FES gene was first discovered as a protein-tyrosine kinase-encoding retroviral oncogene. The ability of v-FES to transform cells in vitro and initiate cancer in vivo has been established by cell culture, engraftment and transgenic mouse studies. The corresponding cellular c-FES proto-oncogene encodes a cytoplasmic FES protein-tyrosine kinase with restrained catalytic activity relative to its retrovirally encoded homologs. These observations have stimulated a search for mutations or inappropriate expression of c-FES in human cancers and research aimed at understanding the functions of the FES kinase and its potential involvement in cancer and other diseases. Paradoxically, although first identified as an oncogene, genetic evidence has also implicated c-fes as a potential tumor suppressor. This review will describe observations from basic and translational research which shapes our current understanding of the physiological, cellular and molecular functions of the FES protein-tyrosine kinase and its potential roles in tumorigenesis. We also propose a model to reconcile the conflicting oncogenic and tumor suppressor roles of c-FES in tumorigenesis.

Targeted inhibition of calpain reduces myocardial hypertrophy and fibrosis in mouse models of type 1 diabetes

OBJECTIVE

Recently we have shown that calpain-1 activation contributes to cardiomyocyte apoptosis induced by hyperglycemia. This study was undertaken to investigate whether targeted disruption of calpain would reduce myocardial hypertrophy and fibrosis in mouse models of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Diabetes in mice was induced by injection of streptozotocin (STZ), and OVE26 mice were also used as a type 1 diabetic model. The function of calpain was genetically manipulated by cardiomyocyte-specific knockout Capn4 in mice and the use of calpastatin transgenic mice. Myocardial hypertrophy and fibrosis were investigated 2 and 5 months after STZ injection or in OVE26 diabetic mice at the age of 5 months. Cultured isolated adult mouse cardiac fibroblast cells were also investigated under high glucose conditions.

RESULTS

Calpain activity, cardiomyocyte cross-sectional areas, and myocardial collagen deposition were significantly increased in both STZ-induced and OVE26 diabetic hearts, and these were accompanied by elevated expression of hypertrophic and fibrotic collagen genes. Deficiency of Capn4 or overexpression of calpastatin reduced myocardial hypertrophy and fibrosis in both diabetic models, leading to the improvement of myocardial function. These effects were associated with a normalization of the nuclear factor of activated T-cell nuclear factor-κB and matrix metalloproteinase (MMP) activities in diabetic hearts. In cultured cardiac fibroblasts, high glucose-induced proliferation and MMP activities were prevented by calpain inhibition.

CONCLUSIONS

Myocardial hypertrophy and fibrosis in diabetic mice are attenuated by reduction of calpain function. Thus targeted inhibition of calpain represents a potential novel therapeutic strategy for reversing diabetic cardiomyopathy.

Calpain mediates pulmonary vascular remodeling in rodent models of pulmonary hypertension, and its inhibition attenuates pathologic features of disease

Pulmonary hypertension is a severe and progressive disease, a key feature of which is pulmonary vascular remodeling. Several growth factors, including EGF, PDGF, and TGF-β1, are involved in pulmonary vascular remodeling during pulmonary hypertension. However, increased knowledge of the downstream signaling cascades is needed if effective clinical interventions are to be developed. In this context, calpain provides an interesting candidate therapeutic target, since it is activated by EGF and PDGF and has been reported to activate TGF-β1. Thus, in this study, we examined the role of calpain in pulmonary vascular remodeling in two rodent models of pulmonary hypertension. These data showed that attenuated calpain activity in calpain-knockout mice or rats treated with a calpain inhibitor resulted in prevention of increased right ventricular systolic pressure, right ventricular hypertrophy, as well as collagen deposition and thickening of pulmonary arterioles in models of hypoxia- and monocrotaline-induced pulmonary hypertension. Additionally, inhibition of calpain in vitro blocked intracellular activation of TGF-β1, which led to attenuated Smad2/3 phosphorylation and collagen synthesis. Finally, smooth muscle cells of pulmonary arterioles from patients with pulmonary arterial hypertension showed higher levels of calpain activation and intracellular active TGF-β. Our data provide evidence that calpain mediates EGF- and PDGF-induced collagen synthesis and proliferation of pulmonary artery smooth muscle cells via an intracrine TGF-β1 pathway in pulmonary hypertension.

Fes tyrosine kinase expression in the tumor niche correlates with enhanced tumor growth, angiogenesis, circulating tumor cells, metastasis, and infiltrating macrophages

Fes is a protein tyrosine kinase with cell autonomous oncogenic activities that are well established in cell culture and animal models, but its involvement in human cancer has been unclear. Abundant expression of Fes in vascular endothelial cells and myeloid cell lineages prompted us to explore roles for Fes in the tumor microenvironment. In an orthotopic mouse model of breast cancer, we found that loss of Fes in the host correlated with reductions in engrafted tumor growth rates, metastasis, and circulating tumor cells. The tumor microenvironment in Fes-deficient mice also showed reduced vascularity and fewer macrophages. In co-culture with tumor cells, Fes-deficient macrophages also poorly promoted tumor cell invasive behavior. Taken together, our observations argue that Fes inhibition might provide therapeutic benefits in breast cancer, in part by attenuating tumor-associated angiogenesis and the metastasis-promoting functions of tumor-associated macrophages.

Calpain 4 is not necessary for LFA-1-mediated function in CD4+ T cells

BACKGROUND

T cell activation and immune synapse formation require the appropriate activation and clustering of the integrin, LFA-1. Previous work has reported that the calpain family of calcium-dependent proteases are important regulators of integrin activation and modulate T cell adhesion and migration. However, these studies have been limited by the use of calpain inhibitors, which have known off-target effects.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we used a LoxP/CRE system to specifically deplete calpain 4, a small regulatory calpain subunit required for expression and activity of ubiquitously expressed calpains 1 and 2, in CD4+ T cells. CD4+ and CD8+ T cells developed normally in Capn4(F/F):CD4-CRE mice and had severely diminished expression of Calpain 1 and 2, diminished talin proteolysis and impaired casein degradation. Calpain 4-deficient T cells showed no difference in adhesion or migration on the LFA-1 ligand ICAM-1 compared to control T cells. Moreover, there was no impairment in conjugation between Capn4(F/F):CD4-CRE T cells and antigen presenting cells, and the conjugates were still capable of polarizing LFA-1, PKC-theta and actin to the immune synapse. Furthermore, T cells from Capn4(F/F):CD4-CRE mice showed normal proliferation in response to either anti-CD3/CD28 coated beads or cognate antigen-loaded splenocytes. Finally, there were no differences in the rates of apoptosis following extrinsic and intrinsic apoptotic stimuli.

CONCLUSION/SIGNIFICANCE

Our findings demonstrate that calpain 4 is not necessary for LFA-1-mediated adhesion, conjugation or migration. These results challenge previous reports that implicate a central role for calpains in the regulation of T cell LFA-1 function.

Abstract 3168: Knock down of m-calpain in a mouse breast carcinoma cell line reduced tumor growth in mouse engraftment studies and compromises the Akt pathway and in vitro cell migration

Calpains are a family of calcium-dependent intracellular cysteine proteases consisting of fourteen members, with µ- and m-calpains (calpain 1 and 2) being ubiquitously expressed. Calpains play crucial roles in a various cellular functions including cell survival, movement and calcium homeostasis. Abnormal expression or activation of calpain is linked to pathological conditions such as neurodegenerative diseases, tumor growth and metastasis, platelet malfunction and muscular dysfunction. Studies have showed that calpain is involved in retraction of focal adhesions at the rear of migrating cells, indicating a major role of calpain in cell movement and cytoskeletal organization. In addition, calpain may be a key component in regulating cell survival and gene expression.

We have examined the role of m-calpain in tumor growth. Mouse mammary carcinoma cells AC2M2 were transduced with a lentiviral vector expressing shRNA directed against m-calpain or a control shRNA. A mouse xenograft experiment was then carried out by injecting control cells or m-calpain knockdown cells into the mammary fat pads of nude mice. Preliminary results showed that mice injected with m-calpain knockdown cells grow smaller tumors. In vitro transwell migration assay showed that the m-calpain knockdown cells migrated slower than the control cells. Furthermore, biochemical studies demonstrated that these AC2M2 m-calpain knockdown cells have reduced activation of key the survival mediator Akt, although there was no significant difference in the growth rate between the knockdown and the control cells. Other biochemical studies implicate the transcription factor Foxo, a downstream target of Akt, in mediating the m-calpain-regulated tumor progression through activation of transcription of genes that are important in cell survival such as p27 Kip1 and Bim. In summary, our current data suggests that m-calpain mediates tumor growth through regulation of Akt signaling. This in turn regulates Foxo in the activation of gene transcription during cell survival signaling.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3168.

Abstract 3890: Induction of cell cycle arrest and apoptosis in mantle cell lymphoma by AZD5438, a novel cyclin-dependent kinase inhibitor

Mantle cell lymphoma (MCL) is recognized as a distinct subtype of B-cell lymphoma and it is characterized by cyclin D1 over-expression, which is caused by t(11;14)(q13;q32) translocation and unregulated cell cycle progression driven by increased cyclin-dependent kinase (CDK) activity. Accordingly, small inhibitors for CDKs represent a potential therapy for MCL. We are investigating a selective small molecule CDK inhibitor, AZD5438, which has nanomolar ranges of IC50 for cyclin E/CDK2, cyclin A/CDK2, cyclin B1/CDK1 and cyclin T/CDK9 and comparing its anti-tumor effects with a pan-CDK inhibitor, Flavopiridol. We hypothesize that inhibition of CDK1/2 by AZD5438 may lead to G1/S and G2 arrest, and therefore inhibit tumor cell proliferation and induce apoptosis in MCL. In Jeko-1 MCL cell lines, AZD5438 has shown both time- and dose-dependent inhibition of cell proliferation, inhibition of the phosphorylation of CDK substrates, and cell cycle arrest in G1 phase. The EC50 for AZD 5438 is 1μM as determined by inhibition of cell viability. We further developed an in vivo MCL xenograft assay: first, to guide the optimization of dosage and dosing schedule for clinical use; and second, to explore the selectivity and potency of this drug using phospho-histone H3 (Ser10) flow cytometry and phosopho-Rb (Ser249/Thr252) immunoblotting as our drug efficacy monitoring system. Recently we have established GFP transduced Jeko-1 cells and inoculated them into 8 to 12 week-old, immune-compromised NOD SCID mice. Investigations of AZD5438 drug dosage in this xenograft model are ongoing. Ultimately, this project is aimed at improving the treatment for MCL patients and reducing the toxic responses to the standard chemotherapeutic regimes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3890.

Abstract 3487: Synergy with combined inhibition of upstream EGFR-HER2 and downstream RAF-MEK nodes in breast cancer cells with activating RAS and RAF mutations

Targeted therapies have been developed to target a variety of oncogenic proteins implicated in breast cancer. These include epidermal growth factor receptor (EGFR), epidermal growth factor receptor type-2 (HER-2), as well as RAS, RAF and MEK, which together comprise the mitogen activated protein kinase (MAPK) cascade. Herein, we explored the therapeutic efficacy of tyrosine kinase inhibitors of EGFR and HER-2 by testing these inhibitors on a human metastatic breast cancer cell line MDA-MB-231. We also determined whether inhibiting tyrosine kinase receptors correlated with the activity of downstream nodes such as MEK and ERK. We report that EGFR inhibitors potently inhibited the phosphorylation of EGFR, but had no effect on MEK and ERK activity, which were observed to be constitutively active in this cell line. Interestingly, MEK/ERK insensitivity correlated with cytotoxic resistance of MDA-MB-231 cells to EGFR inhibitor treatment. In contrast, targeting both EGFR and HER-2 with a dual EGFR/HER-2 inhibitor Lapatinib resulted in significantly improved cytotoxic effects and a partial reduction in MEK and ERK activity. In comparison to the effects of Lapatinib, targeting RAF with Sorafenib resulted in almost complete abrogation of MEK/ERK signaling activity and enhanced cytotoxicity. Our results are consistent with earlier reports suggesting that MAPK signaling is required for MDA-MB-231 cell survival, consistent with the reported presence of activating RAS and RAF mutations in this cell line. Our data highlight the role of RAS and RAF mutations in the uncoupling of downstream nodes (MEK and ERK) from upstream receptor activation. Lastly, the MEK inhibitor U1026 fully inhibited ERK activity but exhibited poor cytotoxicity. This suggests that MDA-MB-231 cells may circumvent MEK inhibition through upstream survival pathways mediated by activated RAS or RAF. An apparent synergistic cytotoxic effect was noted when combining Sorafenib and U1026. Cytotoxic synergy was also observed when Sorafenib was combined with Lapatinib. These putative synergistic drug combinations show promise in that they could deliver significant cytotoxic effects with reduced doses. We find there is merit in targeting multiple oncogenic nodes concurrently to promote additional therapeutic benefits. This also shows potential use in targeting a broader variety of cancer cells that harbor constitutive MAPK signaling associated with oncogenic RAS or RAF mutations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3487.

Abstract 5064: The non-receptor tyrosine kinase Fer is required for activated ErbB2-mediated tumorigenesis

The fer proto-onogene encodes a non-receptor protein-tyrosine kinase (PTK) which together with the parologous Fps/Fes kinase makes up a distinct F-BAR domain containing subclass of PTKs. F-BARs have recently been shown to mediate membrane binding and bending properties that confer roles in receptor endocytosis and vesicle trafficking. Among known substrates of the Fer PTK are cortactin and F-BAR/SH3 containing adaptor proteins that regulate cytoskeletal remodeling and membrane dynamics important to cellular functions such as polarity determination, migration and mitogenesis. Mice deficient in Fer, Fps/Fes or both kinases are overtly healthy; although they do display enhanced responses to endotoxin challenges. Biochemical studies have implicated Fer in growth factor signaling, cadherin-dependent cell-cell adhesion, integrin-mediated adhesion and redox signaling. Cell biological studies have suggested a role for Fer in potentiating proliferation and migration. Recent results in our laboratory have provided compelling biological proof-in-principle that Fer is required for mammary tumorigenesis. RNAi-based knockdown of Fer reduced the tumorigenesis of the metastatic MDA-MB-231 breast cancer cells in mouse xenografting studies. In addition, tumor development in a transgenic mouse model of Her2/Neu/ErbB2-mediated breast tumorigenesis was significantly delayed in Fer-deficient mice by virtue of a targeted knock-in kinase-inactivating mutation in the mouse fer locus. Biochemical internalization assays suggested that EGFR endocytosis was enhanced in Fer-deficient tumor-derived epithelial cell cultures. These data point to a tumor promoting function for Fer in mammary tumorigenesis through a mechanism involving prolongation of ErbB2 signaling. Taken together, these studies suggest that pharmacological intervention of Fer may have therapeutic benefit in human ErbB2 positive breast cancer and potentially, in other epithelial cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5064.

Abstract 3277: The Fps/Fes protein-tyrosine kinase serves a stromal tissue-specific supporting role in an orthotopic mouse model of breast cancer

Fes (also known as Fps) is a cytoplasmic protein tyrosine kinase that is highly expressed in breast epithelial cells during lactation, as well as in vascular endothelial and myeloid cells. Retrovirally encoded oncogenic alleles of Fps/Fes are associated with tumors in chickens and cats and cause tumors in transgenic mice; however, a role for Fes in human cancer has not been established.

We hypothesized that Fes promotes breast tumorigenesis through tumor cell intrinsic functions as well as through functions in stromal tissues including vascular endothelial cells and macrophages. To test the potential tumor cell intrinsic role, AC2M2 cells, a highly metastatic mouse mammary carcinoma cell line, were transduced with expression plasmids encoding wild-type, kinase-inactivated or activated Fes. These cells were then engrafted into the mammary fat pads of nude mice and tumorigenesis was assessed by ultrasound (longitudinal tumor volume measurement), Doppler (tumor-associated vascular flow) and biophotonic imaging of GFP-expressing tumor cells (lung metastasis). There was no obvious difference in tumor growth and angiogenesis at the orthotopic site between each cell line and no apparent difference in lung metastasis. To test the potential stromal role of Fes in breast tumorigenesis, parental AC2M2 cells were injected into the mammary fat pads of wild type and Fes-null nude mice, and tumorigenesis and metastasis were assessed as described above. Wild type mice developed tumors significantly faster than Fes-null mice and there was earlier tumor neovascularization and more recruitment of macrophages. There was also a significantly higher degree of lung metastasis in wild type vs Fes-null mice.

These observations are consistent with a tumor promoting role for Fes acting at the level of the vascular endothelium and macrophages. This might include promoting early tumor neovasularization through direct roles in vascular endothelial cells as well as indirect roles associated with macrophages. The increased metastatic potential also suggests roles in both these cell lineages. This provides genetic evidence that the Fes protein-tyrosine kinase represents a potential novel therapeutic target in breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3277.

Abstract 3269: Calpain knockdown in human breast carcinoma cells reduced xenograft tumor growth rates and inhibited in vitro cell migration and proliferation

Ubiquitously expressed µ- and m-calpain are calcium dependent intracellular cysteine proteases that have been implicated in the regulation of cell proliferation, survival, apoptosis, migration, and invasion. Stable expression and proteolytic activity of the µ- and m-calpain catalytic subunits (encoded by capn1 and capn2 genes, respectively) requires a common regulatory subunit encoded by the capn4/capns1 gene; thus both µ- and m-calpain activities can be blocked by genetic knockout or knockdown of capn4 expression. Calpain is also regulated by an endogenously expressed inhibitor peptide, calpastain.

We screened a panel of human breast cancer and normal epithelial cell lines for expression of calpain and calpastatin. µ- and m-calpain and calpastatin were abundantly expressed in MDA-MB-231, SKBR3, T47D, and MCF-7 breast cancer lines, as well as the normal human breast epithelial cell line MCF-10A.

A stably expressed lentivirally encoded shRNA directed against the capn4 transcript was used to effectively knockdown µ- and m-calpain expression and activity in MDA-MB-231 breast cancer cells. This correlated with attenuated proliferation, migration and invasion, but resistance to anoikis. Biochemical analysis also suggests a role for calpain in the regulation of focal adhesion complex proteins such FAK, PTP-1B, talin and F-actin.

Finally, knockdown of calpain in MDA-MB-231 cells significantly reduced their ability to form tumors when orthotopically injected into the mammary fat pads of nude mice. These observations provide direct genetic evidence that calpain plays a pro-tumorigenic role in the MDA-MB-231 breast cancer cell model system.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3269.

Calcium-dependent plasma membrane repair requires m- or mu-calpain, but not calpain-3, the proteasome, or caspases

Mechanically damaged plasma membrane undergoes rapid calcium-dependent resealing that appears to depend, at least in part, on calpain-mediated cortical cytoskeletal remodeling. Cells null for Capns1, the non-catalytic small subunit present in both m- and mu-calpains, do not undergo calcium-mediated resealing. However, it is not known which of these calpains is needed for repair, or whether other major cytosolic proteinases may participate. Utilizing isozyme-selective siRNAs to decrease expression of Capn1 or Capn2, catalytic subunits of mu- and m-calpains, respectively, in a mouse embryonic fibroblast cell line, we now show that substantial loss of both activities is required to compromise calcium-mediated survival after cell scrape-damage. Using skeletal myotubes derived from Capn3-null mice, we were unable to demonstrate loss of sarcolemma resealing after needle scratch or laser damage. Isolated muscle fibers from Capn3 knockout mice also efficiently repaired laser damage. Employing either a cell line expressing a temperature sensitive E1 ubiquitin ligase, or lactacystin, a specific proteasome inhibitor, it was not possible to demonstrate an effect of the proteasome on calcium-mediated survival after injury. Moreover, several cell-permeant caspase inhibitors were incapable of significantly decreasing survival or inhibiting membrane repair. Taken together with previous studies, the results show that m- or mu-calpain can facilitate repair of damaged plasma membrane. While there was no evidence for the involvement of calpain-3, the proteasome or caspases in early events of plasma membrane repair, our studies do not rule out their participation in downstream events that may link plasma membrane repair to adaptive remodeling after injury.

Calpain-mediated degradation of reversibly oxidized protein-tyrosine phosphatase 1B

Protein-tyrosine phosphatases (PTPs) are regulated by reversible inactivating oxidation of the catalytic-site cysteine. We have previously shown that reversible oxidation upon UVA irradiation is followed by calpain-mediated PTP degradation. Here, we address the mechanism of regulated cleavage and the physiological function of PTP degradation. Reversible oxidation of PTP1B in vitro strongly facilitated the association with calpain and led to greatly increased calpain-dependent inactivating cleavage. Both oxidation-induced association and cleavage depended exclusively on the presence of the catalytic (reversibly oxidized) cysteine residue 215. A major cleavage site was identified preceding amino acid position Ala77. In calpain-deficient cells, insulin signaling was apparently diminished, consistent with a possible role for calpain in removing a negative regulator of insulin signaling. Reversibly oxidized PTP1B may be a target of calpain in this context.

Calpain activation is not required for AIF translocation in PARP-1-dependent cell death (parthanatos)

Apoptosis-inducing factor (AIF) is critical for poly(ADP-ribose) polymerase-1 (PARP-1)-dependent cell death (parthanatos). The molecular mechanism of mitochondrial AIF release to the nucleus remains obscure, although a possible role of calpain I has been suggested. Here we show that calpain is not required for mitochondrial AIF release in parthanatos. Although calpain I cleaved recombinant AIF in a cell-free system in intact cells under conditions where endogenous calpain was activated by either NMDA or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) administration, AIF was not cleaved, and it was released from mitochondria to the nucleus in its 62-kDa uncleaved form. Moreover, NMDA administration under conditions that failed to activate calpain still robustly induced AIF nuclear translocation. Inhibition of calpain with calpastatin or genetic knockout of the regulatory subunit of calpain failed to prevent NMDA- or MNNG-induced AIF nuclear translocation and subsequent cell death, respectively, which was markedly prevented by the PARP-1 inhibitor, 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-iso-quinolinone. Our study clearly shows that calpain activation is not required for AIF release during parthanatos, suggesting that other mechanisms rather than calpain are involved in mitochondrial AIF release in parthanatos.

Apicomplexan parasites co-opt host calpains to facilitate their escape from infected cells

Apicomplexan parasites, including Plasmodium falciparum and Toxoplasma gondii (the causative agents of malaria and toxoplasmosis, respectively), are responsible for considerable morbidity and mortality worldwide. These pathogenic protozoa replicate within an intracellular vacuole inside of infected host cells, from which they must escape to initiate a new lytic cycle. By integrating cell biological, pharmacological, and genetic approaches, we provide evidence that both Plasmodium and Toxoplasma hijack host cell calpain proteases to facilitate parasite egress. Immunodepletion or inhibition of calpain-1 in hypotonically lysed and resealed erythrocytes prevented the escape of P. falciparum parasites, which was restored by adding purified calpain-1. Similarly, efficient egress of T. gondii from mammalian fibroblasts was blocked by either small interfering RNA-mediated suppression or genetic deletion of calpain activity and could be restored by genetic complementation.

The calpain small subunit regulates cell-substrate mechanical interactions during fibroblast migration

Cell migration involves the dynamic formation and release of cell-substrate adhesions, where the exertion and detection of mechanical forces take place. Members of the calpain family of calcium-dependent proteases are believed to have a central role in these processes, possibly through the regulation of focal adhesion dynamics. The ubiquitous calpains, calpain 1 (mu-calpain) and calpain 2 (m-calpain), are heterodimers consisting of large catalytic subunits encoded by the Capn1 and Capn2 genes, respectively, and the small regulatory subunit encoded by Capn4. We have examined the role of the calpain regulatory small subunit in traction force production and mechanosensing during cell migration. Capn4-deficient or rescued cells were plated on flexible polyacrylamide substrates, for both the detection of traction forces and the application of mechanical stimuli. The total force output of Capn4-deficient cells was approximately 75% lower than that of rescued cells and the forces were more randomly distributed and less dynamic in Capn4-deficient cells than in rescued cells. Furthermore, Capn4-deficient cells were less adhesive than wild-type cells and they also failed to respond to mechanical stimulations by pushing or pulling the flexible substrate, or by engaging dorsal receptors to the extracellular matrix. Surprisingly, fibroblasts deficient in calpain 1 or calpain 2 upon siRNA-mediated knockdown of Capn1 or Capn2, respectively, did not show the same defects in force production or adhesion, although they also failed to respond to mechanical stimulation. Interestingly, stress fibers were aberrant and also contained fewer colocalised vinculin-containing adhesions in Capn4-deficient cells than Capn1- and Capn2-knockdown cells. Together, these results suggest that the calpain small subunit plays an important role in the production of mechanical forces and in mediating mechanosensing during fibroblast migration. Furthermore, the Capn4 gene product might perform functions secondary to, or independent of, its role as a regulatory subunit for calpain 1 and calpain 2.

In vivo targeted deletion of calpain small subunit, Capn4, in cells of the osteoblast lineage impairs cell proliferation, differentiation, and bone formation

Calpains are intracellular cysteine proteases, which include widely expressed mu- and m-calpains (1). Both mu-calpains and m-calpains are heterodimers consisting of a large catalytic subunit and a small regulatory subunit. The calpain small subunit encoded by the gene Capn4 directly binds to the intracellular C-terminal tail (C-tail) of the receptor for parathyroid hormone and parathyroid hormone-related peptide and modulates its cellular functions in osteoblasts in vitro (2). To investigate a potential role of the calpain small subunit in osteoblasts in vivo, we generated osteoblast-specific Capn4 knock-out mice using the Cre-LoxP system (3). Mutant mice had smaller bodies with shorter limbs, reduced trabecular bone with thinner cortices, and decreased osteoblast number. In vitro analysis confirmed that deletion of Capn4 in osteoblasts severely affected multiple osteoblast functions including proliferation, differentiation, and matrix mineralization. Collectively, our findings provide the first in vivo demonstration that the calpain small subunit is essential for proper osteoblast activity and bone remodeling.

The Fps/Fes kinase regulates leucocyte recruitment and extravasation during inflammation

Fps/Fes and Fer comprise a distinct subfamily of cytoplasmic protein-tyrosine kinases, and have both been implicated in the regulation of innate immunity. Previous studies showed that Fps/Fes-knockout mice were hypersensitive to systemic lipopolysaccharide (LPS) challenge, and Fer-deficient mice displayed enhanced recruitment of leucocytes in response to localized LPS challenge. We show here for the first time, a role for Fps in the regulation of leucocyte recruitment to areas of inflammation. Using the cremaster muscle intravital microscopy model, we observed increased leucocyte adherence to venules, and increased rates and degrees of transendothelial migration in Fps/Fes-knockout mice relative to wild-type animals subsequent to localized LPS challenge. There was also a decreased vessel wall shear rate in the post-capillary venules of LPS-challenged Fps/Fes-knockout mice, and an increase in neutrophil migration into the peritoneal cavity subsequent to thioglycollate challenge. Using flow cytometry to quantify the expression of surface molecules, we observed prolonged expression of the selectin ligand PSGL-1 on peripheral blood neutrophils from Fps/Fes-knockout mice stimulated ex vivo with LPS. These observations provide important insights into the observed in vivo behaviour of leucocytes in LPS-challenged Fps/Fes-knockout mice and provide evidence that the Fps/Fes kinase plays an important role in the innate immune response.

Fer-mediated cortactin phosphorylation is associated with efficient fibroblast migration and is dependent on reactive oxygen species generation during integrin-mediated cell adhesion

The molecular details linking integrin engagement to downstream cortactin (Ctn) tyrosine phosphorylation are largely unknown. In this report, we show for the first time that Fer and Ctn are potently tyrosine phosphorylated in response to hydrogen peroxide (H2O2) in a variety of cell types. Working with catalytically inactive fer and src/yes/fyn-deficient murine embryonic fibroblasts (ferDR/DR and syf MEF, respectively), we observed that H2O2-induced Ctn tyrosine phosphorylation is primarily dependent on Fer but not Src family kinase (SFK) activity. We also demonstrated for the first time that Fer is activated by fibronectin engagement and, in concert with SFKs, mediates Ctn tyrosine phosphorylation in integrin signaling pathways. Reactive oxygen species (ROS) scavengers or the NADPH oxidase inhibitor, diphenylene iodonium, attenuated integrin-induced Fer and Ctn tyrosine phosphorylation. Taken together, these findings provide novel genetic evidence that a ROS-Fer signaling arm contributes to SFK-mediated Ctn tyrosine phosphorylation in integrin signaling. Lastly, a migration defect in ferDR/DR MEF suggests that integrin signaling through the ROS-Fer-Ctn signaling arm may be linked to mechanisms governing cell motility. These data demonstrate for the first time an oxidative link between integrin adhesion and an actin-binding protein involved in actin polymerization.

Sequential activation of poly(ADP-ribose) polymerase 1, calpains, and Bax is essential in apoptosis-inducing factor-mediated programmed necrosis

Alkylating DNA damage induces a necrotic type of programmed cell death through the poly(ADP-ribose) polymerases (PARP) and apoptosis-inducing factor (AIF). Following PARP activation, AIF is released from mitochondria and translocates to the nucleus, where it causes chromatin condensation and DNA fragmentation. By employing a large panel of gene knockout cells, we identified and describe here two essential molecular links between PARP and AIF: calpains and Bax. Alkylating DNA damage initiated a p53-independent form of death involving PARP-1 but not PARP-2. Once activated, PARP-1 mediated mitochondrial AIF release and necrosis through a mechanism requiring calpains but not cathepsins or caspases. Importantly, single ablation of the proapoptotic Bcl-2 family member Bax, but not Bak, prevented both AIF release and alkylating DNA damage-induced death. Thus, Bax is indispensable for this type of necrosis. Our data also revealed that Bcl-2 regulates N-methyl-N'-nitro-N'-nitrosoguanidine-induced necrosis. Finally, we established the molecular ordering of PARP-1, calpains, Bax, and AIF activation, and we showed that AIF downregulation confers resistance to alkylating DNA damage-induced necrosis. Our data shed new light on the mechanisms regulating AIF-dependent necrosis and support the notion that, like apoptosis, necrosis could be a highly regulated cell death program.