Three-dimensional growth sensitizes breast cancer cells to treatment with ferroptosis-promoting drugs

Drugs causing ferroptosis, iron-mediated cell death, represent promising tools for cancer treatment. While exploring the effect of these drugs on breast cancer (BC), we found that a ferroptosis-inducing drug erastin dramatically inhibits tumorigenicity of human BC cells in mice but when used at a concentration known to effectively kill other cell types only modestly reduces such growth in 2D monolayer culture. BCs grow in vivo as 3D masses, and we found that ferroptosis inducers erastin and sulfasalazine inhibit growth of multiple human BC cell lines in 3D culture significantly stronger than in 2D culture. To understand the mechanism of this differential effect, we found that ferroptosis inducers upregulate mRNAs encoding multiple direct and indirect autophagy stimulators, such as ATG16L2, ATG9A, ATG4D, GABARAP, SQSTM/p62, SEC23A and BAX, in tumor cells growing in 2D but not in 3D culture. Furthermore, these drugs promoted autophagy of tumor cells growing in a 2D but not in a 3D manner. We observed that pharmacological inhibition of autophagy-stimulating protein kinase ULK1 or RNA interference-mediated knockdown of autophagy mediator ATG12 significantly sensitized tumor cells to erastin treatment in 2D culture. We also found that ferroptosis-promoting treatments upregulate heme oxygenase-1 (HO-1) in BC cells. HO-1 increases cellular free iron pool and can potentially promote ferroptosis. Indeed, we observed that HO-1 knockdown by RNA interference reversed the effect of ferroptosis inducers on BC cell 3D growth. Hence, the effect of these drugs on such growth is mediated by HO-1. In summary, autophagy triggered by ferroptosis-promoting drugs reduces their ability to kill BC growing in a 2D manner. This protection mechanism is inhibited in BC cells growing as a 3D mass, and ferroptosis-promoting drugs kill such cells more effectively. Moreover, this death is mediated by HO-1. Thus, ferroptosis induction represents a promising strategy for blocking 3D BC growth.

ErbB2/Her2-dependent downregulation of a cell death-promoting protein BLNK in breast cancer cells is required for 3D breast tumor growth

A significant proportion of breast cancers are driven by ErbB2/Her2 oncoprotein that they overexpress. These malignancies are typically treated with various ErbB2-targeted drugs, but many such cancers develop resistance to these agents and become incurable. Conceivably, treatment of ErbB2-positive cancers could be facilitated by use of agents blocking oncogenic signaling mechanisms downstream of ErbB2. However, current understanding of these mechanisms is limited. The ability of solid tumor cells to resist anoikis, cell death triggered by cell detachment from the extracellular matrix (ECM), is thought to be critical for 3D tumor growth. In an effort to understand the mechanisms of ErbB2-driven breast cancer cell anoikis resistance we found that detachment of non-malignant breast epithelial cells from the ECM upregulates a cell death-promoting tumor suppressor adapter protein BLNK and that ErbB2 blocks this upregulation by reducing tumor cell levels of transcription factor IRF6. We further observed that trastuzumab, a therapeutic anti-ErbB2 antibody, upregulates BLNK in human trastuzumab-sensitive but not trastuzumab-resistant ErbB2-positive breast cancer cells. Moreover, we established that BLNK promotes anoikis by activating p38 MAP kinase and that ErbB2-dependent BLNK downregulation blocks breast cancer cell anoikis. In search for pharmacological approaches allowing to upregulate BLNK in tumor cells we found that clinically approved proteasome inhibitor bortezomib upregulates IRF6 and BLNK in human breast cancer cells and inhibits their 3D growth in a BLNK-dependent manner. In addition, we found that BLNK upregulation in human ErbB2-positive breast cancer cells blocks their ability to form tumors in mice. Furthermore, we used publicly available data on mRNA levels in multiple breast cancers to demonstrate that increased BLNK mRNA levels correlate with increased relapse-free survival in a cohort of approximately 400 patients with ErbB2-positive breast cancer. In summary, we discovered a novel mechanism of ErbB2-driven 3D breast tumor growth mediated by ErbB2-dependent BLNK downregulation.

Tumor levels of the mediators of ErbB2-driven anoikis resistance correlate with breast cancer relapse in patients receiving trastuzumab-based therapies

PURPOSE

Patients with ErbB2/Her2 oncoprotein-positive breast cancers often receive neoadjuvant therapies (NATs) containing the anti-ErbB2 antibody trastuzumab. Tumors that are still present after NATs are resected, and patients continue receiving trastuzumab. These cancers are associated with high relapse risk. Whether relapse will occur cannot be presently reliably predicted. The ability to make such predictions could improve disease management. We found previously that ErbB2 blocks breast tumor cell anoikis, apoptosis induced by cell detachment from the extracellular matrix, by downregulating the pro-apoptotic protein Irf6 and upregulating the anti-apoptotic protein Epidermal Growth Factor Receptor (EGFR) in the cells and, thus, promotes their three-dimensional growth. We now tested whether tumor levels of these proteins before and after NATs correlate with patients' relapse-free survival (RFS) and overall survival (OS).

METHODS

We selected archival breast tumor samples collected from 37 women with ErbB2-positive stages II and III breast cancer before and after NATs. We used immunohistochemistry to test whether levels of the indicated proteins in respective tumors correlate with RFS and OS.

RESULTS

We observed that the presence of high Irf6 levels in the tumors following NATs correlated with reduced RFS and OS. Perhaps not by coincidence, we noticed that trastuzumab-sensitive ErbB2-positive breast cancer cells selected for the ability to overproduce exogenous Irf6 in culture acquired trastuzumab resistance. Finally, EGFR presence in patients' tumors before or after NATs was associated with decreased RFS and OS.

CONCLUSIONS

This study could help identify patients with ErbB2-positive tumors that are at increased risk of disease relapse following NATs.

Trastuzumab-induced upregulation of a protein set in extracellular vesicles emitted by ErbB2-positive breast cancer cells correlates with their trastuzumab sensitivity

Background

ErbB2/HER2 oncoprotein often drives breast cancers (BCs) which are treated with the anti-ErbB2 antibody trastuzumab. The efficacy of trastuzumab-based metastatic BC therapies is routinely assessed by imaging studies. Trastuzumab typically becomes ineffective in the case of this disease and is then replaced by other drugs. Biomarkers of BC trastuzumab response could allow imaging studies and the switch to other drugs to occur earlier than is now possible. Moreover, bone-only BC metastases can be hard to measure, and biomarkers of their trastuzumab response could facilitate further treatment decisions. Such biomarkers are presently unavailable. In this study, we searched for proteins whose levels in BC cell-emitted extracellular vesicles (EVs) potentially correlate with BC trastuzumab sensitivity.

Methods

We isolated EVs from cultured trastuzumab-sensitive and trastuzumab-resistant human BC cells before and after trastuzumab treatment and characterized these EVs by nanoparticle tracking analysis and electron microscopy. We found previously that ErbB2 drives BC by downregulating a pro-apoptotic protein PERP. We now tested whether trastuzumab-induced PERP upregulation in EVs emitted by cultured human BC cells correlates with their trastuzumab sensitivity. We also used mass spectrometry to search for additional proteins whose levels in such EVs reflect BC cell trastuzumab sensitivity. Once we identified proteins whose EV levels correlate with this sensitivity in culture, we explored the feasibility of testing whether their levels in the blood EVs of trastuzumab-treated metastatic BC patients correlate with patients’ response to trastuzumab-based treatments.

Results

We found that neither trastuzumab nor acquisition of trastuzumab resistance by BC cells affects the size or morphology of EVs emitted by cultured BC cells. We established that EV levels of proteins PERP, GNAS2, GNA13, ITB1, and RAB10 correlate with BC cell trastuzumab response. Moreover, these proteins were upregulated during trastuzumab-based therapies in the blood EVs of a pilot cohort of metastatic BC patients that benefited from these therapies but not in those derived from patients that failed such treatments.

Conclusions

Upregulation of a protein set in EVs derived from cultured breast tumor cells correlates with tumor cell trastuzumab sensitivity. It is feasible to further evaluate these proteins as biomarkers of metastatic BC trastuzumab response.

Oncogenic RAS-induced downregulation of ATG12 is required for survival of malignant intestinal epithelial cells

Activating mutations of RAS GTPase contribute to the progression of many cancers, including colorectal carcinoma. So far, attempts to develop treatments of mutant RAS-carrying cancers have been unsuccessful due to insufficient understanding of the salient mechanisms of RAS signaling. We found that RAS downregulates the protein ATG12 in colon cancer cells. ATG12 is a mediator of autophagy, a process of degradation and reutilization of cellular components. In addition, ATG12 can kill cells via autophagy-independent mechanisms. We established that RAS reduces ATG12 levels in cancer cells by accelerating its proteasomal degradation. We further observed that RAS-dependent ATG12 loss in these cells is mediated by protein kinases MAP2K/MEK and MAPK1/ERK2-MAPK3/ERK1, known effectors of RAS. We also demonstrated that the reversal of the effect of RAS on ATG12 achieved by the expression of exogenous ATG12 in cancer cells triggers both apoptotic and nonapoptotic signals and efficiently kills the cells. ATG12 is known to promote autophagy by forming covalent complexes with other autophagy mediators, such as ATG5. We found that the ability of ATG12 to kill oncogenic RAS-carrying malignant cells does not require covalent binding of ATG12 to other proteins. In summary, we have identified a novel mechanism by which oncogenic RAS promotes survival of malignant intestinal epithelial cells. This mechanism is driven by RAS-dependent loss of ATG12 in these cells.

Mek activity is required for ErbB2 expression in breast cancer cells detached from the extracellular matrix

Detachment of non-malignant epithelial cells from the extracellullar matrix (ECM) triggers their growth arrest and apoptosis. Conversely, carcinoma cells can grow without adhesion to the ECM. This capacity for anchorage-independent growth is thought to be critical for tumor progression. ErbB2/Her2 oncoprotein is overproduced by a significant fraction of breast cancers and promotes anchorage-independent tumor cell growth by poorly understood mechanisms. In an effort to understand them we found that in order to produce ErbB2, detached breast cancer cells require the activity of an ErbB2 effector protein kinase Mek and that Mek-driven ErbB2 expression is neccesary for anchorage-independent growth of such cells. We observed that Mek inhibition does not alter ErbB2 mRNA levels in detached cancer cells and that ErbB2 protein loss induced by this inhibition can be blocked by a lysosomal inhibitor. We also noticed that an increase of the density of cancer cells detached from the ECM downregulates a Mek effector protein kinase Erk and causes ErbB2 loss. Those cells that survive after ErbB2 loss display resistance to trastuzumab, an anti-ErbB2 antibody used for ErbB2-positive breast cancer treatment. Thus, Mek-induced ErbB2 stabilization in detached breast cancer cells is critical for their ability to grow anchorage-independently and their trastuzumab sensitivity.

ErbB2-dependent downregulation of a pro-apoptotic protein Perp is required for oncogenic transformation of breast epithelial cells

The ability of breast cancer cells to resist anoikis, apoptosis caused by detachment of the non-malignant epithelial cells from the extracellular matrix (ECM), is thought to be critical for breast tumor growth, invasion and metastasis. ErbB2, an oncoprotein that is often overproduced in breast tumors, can block breast cancer cell anoikis via mechanisms that are understood only in part. In an effort to understand them better we found that detachment of the non-malignant human breast epithelial cells from the ECM upregulates a protein Perp in these cells. Perp is a component of the desmosomes, multiprotein complexes involved in cell-to-cell adhesion. Perp can cause apoptosis via unknown mechanisms. We demonstrated that Perp upregulation by cell detachment is driven by detachment-induced loss of epidermal growth factor receptor (EGFR). We also found that Perp knockdown by RNA interference (RNAi) rescues detached cells from death which indicates that Perp contributes to their anoikis. We observed that ErbB2, when overexpressed in detached breast epithelial cells, causes Perp downregulation. Furthermore, ErbB2-directed RNAi or treatment with lapatinib, an ErbB2/EGFR small-molecule inhibitor used for breast cancer therapy, upregulated Perp in ErbB2-positive human breast and ovarian carcinoma cells. We established that ErbB2 downregulates Perp by activating an ErbB2 effector protein kinase Mek that blocks detachment-induced EGFR loss in a manner that requires the presence of a signaling protein Sprouty-2. Finally, we observed that restoration of the wild-type Perp levels in ErbB2-overproducing breast epithelial cells increases their anoikis susceptibility and blocks their clonogenicity in the absence of adhesion to the ECM. In summary, we have identified a novel mechanism of ErbB2-mediated mechanism of anoikis resistance of ErbB2-overproducing breast epithelial cells. This mechanism allows such cells to grow without adhesion to the ECM and is driven by ErbB2-induced activation of Mek, subsequent EGFR upregulation and further EGFR-dependent Perp loss.

Upregulation of ATG3 contributes to autophagy induced by the detachment of intestinal epithelial cells from the extracellular matrix, but promotes autophagy-independent apoptosis of the attached cells

Detachment of nonmalignant intestinal epithelial cells from the extracellular matrix (ECM) triggers their growth arrest and, ultimately, apoptosis. In contrast, colorectal cancer cells can grow without attachment to the ECM. This ability is critical for their malignant potential. We found previously that detachment-induced growth arrest of nonmalignant intestinal epithelial cells is driven by their detachment-triggered autophagy, and that RAS, a major oncogene, promotes growth of detached cells by blocking such autophagy. In an effort to identify the mechanisms of detachment-induced autophagy and growth arrest of nonmalignant cells we found here that detachment of these cells causes upregulation of ATG3 and that ATG3 upregulation contributes to autophagy and growth arrest of detached cells. We also observed that when ATG3 expression is artificially increased in the attached cells, ATG3 promotes neither autophagy nor growth arrest but triggers their apoptosis. ATG3 upregulation likely promotes autophagy of the detached but not that of the attached cells because detachment-dependent autophagy requires other detachment-induced events, such as the upregulation of ATG7. We further observed that those few adherent cells that do not die by apoptosis induced by ATG3 become resistant to apoptosis caused by cell detachment, a property that is critical for the ability of normal epithelial cells to become malignant. We conclude that cell-ECM adhesion can switch ATG3 functions: when upregulated in detached cells in the context of other autophagy-promoting events, ATG3 contributes to autophagy. However, when overexpressed in the adherent cells, in the circumstances not favoring autophagy, ATG3 triggers apoptosis.

Anoikis of colon carcinoma cells triggered by β-catenin loss can be enhanced by tumor necrosis factor receptor 1 antagonists

Detachment of non-malignant epithelial cells from the extracellular matrix causes their apoptosis, a phenomenon called anoikis. By contrast, carcinoma cells are anoikis-resistant, and this resistance is thought to be critical for tumor progression. Many oncogenes trigger not only anti- but also pr-apoptotic signals. The proapoptotic events represent an aspect of a phenomenon called oncogenic stress, which acts as a safeguard mechanism blocking tumor initiation. In cells that become malignant, oncogene-induced antiapoptotic signals outbalance the proapoptotic ones. It is now thought that treatments blocking the antiapoptotic events but preserving the proapoptotic signals can be particularly effective in killing tumor cells. Whether or not oncogenes induce any proanoikis signals that can be used for enhancing the efficiency of approaches aimed at triggering anoikis of cancer cells has never been explored. β-Catenin is a major oncoprotein that is often activated in colorectal cancer and promotes tumor progression via mechanisms that are understood only in part. We found here that β-catenin triggers both anti- and proanoikis signals in colon cancer cells. We observed that the antianoikis signals prevail and the cells become anoikis-resistant. We further established that one proanoikis signal in these cells is triggered by β-catenin-induced downregulation of an apoptosis inhibitor tumor necrosis factor receptor 1 (TNFR1) and subsequent reduction of the activity of a transcription factor NF-κB (nuclear factor-κB), a mediator of TNFR1 signaling. We also found that the effect of β-catenin on TNFR1 requires the presence of transcription factor TCF1, a β-catenin effector. We demonstrated that ablation of β-catenin in colon cancer cells triggers their anoikis and that this anoikis is enhanced even further if low TNFR1 or NF-κB activity is artificially preserved in the β-catenin-deprived cells. Thus, inhibition of TNFR1 or NF-κB activity can be expected to enhance the efficiency of approaches aimed at blocking β-catenin-driven anoikis resistance of colon carcinoma cells.

ras-Induced up-regulation of CTP:phosphocholine cytidylyltransferase α contributes to malignant transformation of intestinal epithelial cells

Cancer cells have enhanced lipogenic capacity characterized by increased synthesis of fatty acids and complex lipids, including phosphatidylcholine (PC). As the rate-limiting enzyme in the CDP-choline pathway for PC synthesis, CTP:phosphocholine cytidylyltransferase α (CCTα) is implicated in the provision of membranes and bioactive lipids necessary of cell proliferation. In this study, we assessed the role of CCTα in malignant intestinal epithelial cells transformed with activated H-ras (IEC-ras). Three IEC-ras clones had significant up-regulation CCTα expression, but PC synthesis and in vitro activity of CCTα were similar to control IEC. RNA interference of CCTα in adherent IEC-ras did not affect PC synthesis, confirming that the enzyme was relatively inactive. However, CCTα silencing in ras-transformed IEC reduced anchorage-independent growth, a criterion for malignant transformation, as well as tumorigenicity in mice. Relative to their adherent counterparts, detached IEC-ras had increased PC synthesis that was attenuated by inducible CCTα silencing. Detachment of IEC-ras was accompanied by increased CCTα phosphorylation and cytosolic enzyme activity. We conclude that the expanded pool of CCTα in IEC-ras is activated by detachment. This provides the increased PC biosynthetic capacity that contributes to malignant transformation of intestinal epithelial cells when detached from the extracellular matrix.

Tumor suppressor protein kinase Chk2 is a mediator of anoikis of intestinal epithelial cells

Resistance of carcinoma cells to anoikis, apoptosis that is normally induced by detachment of nonmalignant epithelial cells from the extracellular matrix, is thought to be critical for carcinoma progression. Molecular mechanisms that control anoikis of nonmalignant and cancer cells are understood poorly. In an effort to understand them we found that detachment of nonmalignant intestinal epithelial cells triggers upregulation of Chk2, a pro-apoptotic protein kinase that has never been implicated in anoikis and has been thought to kill cells mainly under the conditions compromising genome integrity. We found that enforced downregulation of Chk2 protects intestinal epithelial cells from anoikis. Chk2 can kill cells by stabilizing p53 tumor suppressor protein or via p53-independent mechanisms, and we established that Chk2-mediated anoikis of intestinal epithelial cells is p53-independent. We further found that, unlike nonmalignant intestinal epithelial cells whose anoikis is triggered by detachment-induced Chk2 upregulation, intestinal epithelial cells carrying oncogenic ras, a known inhibitor of anoikis, remain anoikis-resistant in response to enforced Chk2 upregulation. By contrast, drugs, such as topoisomerase I inhibitors, that can kill cells via Chk2-indpendent mechanisms, efficiently triggered anoikis of ras-transformed cells. Thus, oncogenic ras can prevent Chk2 from triggering anoikis even when levels of this protein kinase are elevated in cancer cells, and the use of therapeutic agents that kill cells in a Chk-2-independent, rather than Chk-2-dependent, manner could represent an efficient strategy for overcoming ras-induced anoikis resistance of these cells. We conclude that Chk-2 is an important novel component of anoikis-promoting machinery of intestinal epithelial cells.

Oncogenic ras-induced down-regulation of pro-apoptotic protease caspase-2 is required for malignant transformation of intestinal epithelial cells

Resistance of carcinoma cells to anoikis, apoptosis that is normally induced by loss of cell-to-extracellular matrix adhesion, is thought to be essential for the ability of these cells to form primary tumors, invade adjacent tissues, and metastasize to distant organs. Current knowledge about the mechanisms by which cancer cells evade anoikis is far from complete. In an effort to understand these mechanisms, we found that ras, a major oncogene, down-regulates protease caspase-2 (which initiates certain steps of the cellular apoptotic program) in malignant human and rat intestinal epithelial cells. This down-regulation could be reversed by inhibition of a protein kinase Mek, a mediator of Ras signaling. We also found that enforced down-regulation of caspase-2 in nonmalignant intestinal epithelial cells by RNA interference protected them from anoikis. Furthermore, the reversal of the effect of Ras on caspase-2 achieved by the expression of exogenous caspase-2 in detached ras-transformed intestinal epithelial cells promoted well established apoptotic events, such as the release of the pro-apoptotic mitochondrial factors cytochrome c and HtrA2/Omi into the cytoplasm of these cells, significantly enhanced their anoikis susceptibility, and blocked their long term growth in the absence of adhesion to the extracellular matrix. Finally, the blockade of the effect of Ras on caspase-2 substantially suppressed growth of tumors formed by the ras-transformed cells in mice. We conclude that ras-induced down-regulation of caspase-2 represents a novel mechanism by which oncogenic Ras protects malignant intestinal epithelial cells from anoikis, promotes their anchorage-independent growth, and allows them to form tumors in vivo.

Oncogenic ras-induced down-regulation of autophagy mediator Beclin-1 is required for malignant transformation of intestinal epithelial cells

Detachment of non-malignant epithelial cells from the extracellular matrix causes their growth arrest and, ultimately, death. By contrast, cells composing carcinomas, cancers of epithelial origin, can survive and proliferate without being attached to the extracellular matrix. These properties of tumor cells represent hallmarks of malignant transformation and are critical for cancer progression. Previously we identified several mechanisms by which ras, a major oncogene, blocks detachment-induced apoptosis of intestinal epithelial cells, but mechanisms by which Ras promotes proliferation of those cells that remain viable following detachment are unknown. We show here that detachment of non-malignant intestinal epithelial cells promotes formation of autophagosomes, vacuole-like structures that mediate autophagy (a process of cellular self-cannibalization), and that oncogenic ras prevents this autophagosome formation. We also found that ras activates a GTPase RhoA, that RhoA promotes activation of a protease calpain, and that calpain triggers degradation of Beclin-1, a critical mediator of autophagy, in these cells. The reversal of the effect of ras on Beclin-1 (achieved by expression of exogenous Beclin-1) promoted autophagosome formation following cell detachment, significantly reduced the fraction of detached cells in the S phase of the cell cycle and their rate of proliferation without affecting their viability. Furthermore, RNA interference-induced Beclin-1 down-regulation in non-malignant intestinal epithelial cells prevented detachment-dependent reduction of the fraction of these cells in the S phase of the cell cycle. Thus, ras oncogene promotes proliferation of those malignant intestinal epithelial cells that remain viable following detachment via a distinct novel mechanism that involves Ras-induced down-regulation of Beclin-1.

Down-regulation of death-associated protein kinase-2 is required for beta-catenin-induced anoikis resistance of malignant epithelial cells

Resistance of solid tumor cells to anoikis, apoptosis induced by cell detachment from the extracellular matrix, is thought to be critical for the ability of these cells to grow anchorage independently within three-dimensional tumor masses and from metastases. Beta-catenin, a major oncoprotein, can inhibit anoikis of cancer cells via unknown mechanisms. In an effort to identify these mechanisms we found that beta-catenin blocks anoikis of malignant kidney and intestinal epithelial cells and promotes their anchorage-independent growth by down-regulating death-associated protein kinase-2 (DAPk-2), a pro-apoptotic protein whose cellular functions have so far remained unexplored. We found that beta-catenin-induced down-regulation of DAPk-2 requires the presence of the transcription factor Tcf-4, a known mediator of beta-catenin signaling. We also observed that DAPk-2 contributes to the execution of anoikis of the non-malignant epithelial cells. Thus, beta-catenin-induced down-regulation of DAPk-2 represents a novel signaling mechanism by which beta-catenin promotes the survival of malignant epithelial cells following their detachment from the ECM and enables these cells to grow in an anchorage-independent manner.

Acquisition of anoikis resistance promotes the emergence of oncogenic K-ras mutations in colorectal cancer cells and stimulates their tumorigenicity in vivo

Detachment from the extracellular matrix causes apoptosis of normal epithelial cells--a phenomenon called anoikis. K-ras oncogene, an established anoikis inhibitor, often occurs in colorectal carcinoma (CRC). In addition to blocking anoikis-inducing mechanisms, oncogenic K-ras can cause anoikis-unrelated changes in CRC cells, such as induction of events promoting their deregulated mitogenesis, ability to trigger angiogenesis, and so on. Thus, whether ras-induced anoikis resistance of CRC cells is essential for their ability to form tumors in vivo or represents a mere epiphenomenon is unclear. We found that when poorly tumorigenic, oncogenic, K-ras-negative, anoikis-susceptible human CRC cells were cultured under anoikis-inducing conditions in vitro, they spontaneously gave rise to an anoikis-resistant cell population harboring de novo oncogenic K-ras mutations and manifesting dramatically increased tumorigenicity. We further observed that a variant of the same oncogenic K-ras-negative anoikis-susceptible cells selected for increased tumorigenicity acquired de novo oncogenic K-ras mutations and manifested increased anoikis resistance. Unlike the case with anoikis, oncogenic K-ras did not rescue CRC cells from death caused by hypoxia or anticancer agents. Taken collectively, our results support the notion that ras-induced anoikis resistance of CRC cells is essential for their ability to form tumors in vivo and thus represents a potential therapeutic target.

Detachment-induced upregulation of XIAP and cIAP2 delays anoikis of intestinal epithelial cells

Detachment of normal epithelial cells from the extracellular matrix triggers apoptosis, a phenomenon called anoikis. Conversely, carcinoma cells tend to be relatively more anoikis-resistant than their normal counterparts, and this increased resistance represents a critical feature of the malignant phenotype. Mechanisms that control susceptibility and resistance to anoikis are not fully understood. It is now known that detachment of non-malignant epithelial cells triggers both pro- and antiapoptotic signals, and it is the balance between these signals and the duration of detachment that determine further fate of the cells. Detachment-induced antiapoptotic events delay anoikis and if cells reattach relatively soon after detachment they survive. Direct regulators of apoptosis responsible for this delay of anoikis are unknown. We found that detachment of non-malignant intestinal epithelial cells triggers upregulation of inhibitors of apoptosis protein (IAP) family, such as X-chromosome-linked inhibitor of apoptosis protein and cellular inhibitor of apoptosis-2 (cIAP2). We demonstrated that this upregulation requires detachment-dependent activation of the transcription factor nuclear factor-kappaB. We further observed that various IAP antagonists accelerate anoikis, indicating that upregulation of the IAPs delays detachment-triggered apoptosis. We conclude that the IAPs are important regulators of the balance between detachment-triggered life and death signals. Perhaps, not by coincidence, these proteins are often upregulated in carcinomas, tumors composed of cells that tend to be anoikis-resistant.

ras Oncogene triggers up-regulation of cIAP2 and XIAP in intestinal epithelial cells: epidermal growth factor receptor-dependent and -independent mechanisms of ras-induced transformation

Detachment of normal epithelial cells from the extracellular matrix (ECM) triggers apoptosis, a phenomenon called anoikis. Conversely, carcinomas (cancers of epithelial origin) represent three-dimensional disorganized multicellular masses in which cells are deprived of adhesion to the ECM but remain viable. Resistance of cancer cells to anoikis is thought to be critical for tumor progression. However, the knowledge about molecular mechanisms of this type of resistance remains limited. Herein we report that ras oncogene, an established inhibitor of anoikis, triggers a significant upregulation of anti-apoptotic proteins cIAP2 and XIAP in intestinal epithelial cells. We also observed that the effect of ras on cIAP2 requires ras-induced autocrine production of transforming growth factor alpha (TGF-alpha), a ligand for epidermal growth factor receptor, whereas ras-triggered up-regulation of XIAP is TGF-alpha-independent. Moreover, overexpression of either cIAP2 or XIAP in nonmalignant intestinal epithelial cell was found to block anoikis. In addition, an established IAP antagonist Smac or Smac-derived cell-permeable peptide suppressed ras-induced anoikis resistance and subsequent anchorage-independent growth of ras-transformed cells. We conclude that ras-induced overexpression of cIAP2 and XIAP significantly contributes to the ability of ras-transformed intestinal epithelial cells to survive in the absence of adhesion to the ECM and grow in a three-dimensional manner.

Photoaffinity labeling of 30S-subunit proteins S7 and S11 by 4-thiouridine-substituted tRNA(Phe) situated at the P site of Escherichia coli ribosomes

4-Thiouridine, a photoreactive analogue of uridine, was randomly incorporated into yeast tRNA(Phe) precursor molecules by transcription with T7 RNA polymerase and the resulting transcripts were converted into mature tRNA(Phe) by treatment with RNase P RNA. The photoreactive tRNA(Phe) was aminoacylated and bound to the P site of Escherichia coli 70S ribosomes in the presence of a poly(U) template. Irradiation of the complexes with light of 300 nm resulted in the covalent crosslinking of nt U20 in the D loop of the tRNA to protein S11 of the 30S ribosomal subunit, whereas nt U33 in the anticodon loop crosslinked to 30S-subunit protein S7. These results allowed us to map the D loop of P site-bound tRNA to the platform of the 30S ribosomal subunit and provided additional information about contacts between protein S7 and the anticodon loop in the cleft between the platform and the subunit head.

Peptidyl transferase and beyond

The peptidyl transferase center of the Escherichia coli ribosome encompasses a number of 50S-subunit proteins as well as several specific segments of the 23S rRNA. Although our knowledge of the role that both ribosomal proteins and 23S rRNA play in peptide bond formation has steadily increased, the location, organization, and molecular structure of the peptidyl transferase center remain poorly defined. Over the past 10 years, we have developed a variety of photoaffinity reagents and strategies for investigating the topography of tRNA binding sites on the ribosome. In particular, we have used the photoreactive tRNA probes to delineate ribosomal components in proximity to the 3' end of tRNA at the A, P, and E sites. In this article, we describe recent experiments from our laboratory which focus on the identification of segments of the 23S rRNA at or near the peptidyl transferase center and on the functional role of L27, the 50S-subunit protein most frequently labeled from the acceptor end of A- and P-site tRNAs. In addition, we discuss how these results contribute to a better understanding of the structure, organization, and function of the peptidyl transferase center.

Investigation into the relationship between personality traits and OCD

In the light of recent research suggesting that obsessive-compulsive disorder is more likely to be associated with constellations of personality traits other than obsessive-compulsive personality traits, the present study was undertaken to explore this relationship further and to remove the possibly confounding effects of general pathology, anxiety and depression. By using a non-clinical sample and partialling out the effects of anxiety and depression, it was found, contrary to recent research, that specific obsessional symptoms were only related to the traits of obsessive-compulsive personality disorder.

Recombinant photoreactive tRNA molecules as probes for cross-linking studies

Photoreactive tRNA derivatives have been used extensively for investigating the interaction of tRNA molecules with their ligands and substrates. Recombinant RNA technology facilitates the construction of such tRNA probes through site-specific incorporation of photoreactive nucleosides. The general strategy involves preparation of suitable tRNA fragments and their ligation either to a photoreactive nucleotide or to each other. tRNA fragments can be prepared by site-specific cleavage of native tRNAs, or synthesized by enzymatic and chemical means. A number of photoreactive nucleosides suitable for incorporation into tRNA are presently available. Joining of tRNA fragments is accomplished either by RNA ligase or by DNA ligase in the presence of a DNA splint. The application of this methodology to the study of tRNA binding sites on the ribosome is discussed, and a model of the tRNA-ribosome complex is presented.

Mapping the central fold of tRNA2(fMet) in the P site of the Escherichia coli ribosome

4-Thiouridine (s4U), a photoreactive analog of uridine, was randomly incorporated into tRNA2(fMet) precursor molecules by transcription with T7 RNA polymerase. The s4U-containing transcripts were trimmed at their 5'-ends with RNase P RNA to yield mature tRNA2(fMet). The photoreactive tRNA2(fMet) derivatives were aminoacylated and bound to the P site of 70S ribosomes from Escherichia coli in the presence of a poly(A,G,U) template. Irradiation of the complexes at 300 nm resulted in the covalent cross-linking of tRNA2(fMet) to ribosomal proteins and rRNAs within both the 50S and 30S subunits. The labeled proteins were identified as L1, L27, and S19. 50S-subunit proteins L1 and L27 were attached to nucleotide U17 or U17.1 within the D loop of tRNA2(fMet), whereas 30S-subunit protein S19 was cross-linked to nucleotide U47 in the variable loop. Both of these sites occur in or near the central fold of the tRNA. These results permit us to map the D loop of P site-bound tRNA to the region between the central protuberance and the L1 ridge on the 50S ribosomal subunit, while the variable loop can be placed above the cleft on the head of the 30S subunit.

Identification of the Escherichia coli 30S ribosomal subunit protein neighboring mRNA during initiation of translation

To identify the proteins of the 30S ribosomal subunit of E coli that neighbor mRNA in the ternary initiation complex (mRNA*30S subunit*tRNA(fMet), we used an affinity cross-linking approach in which photoactivated groups were attached to different positions along the mRNA chain. A series of mini-genes originating from the 5'-end region of the cro gene of lambda bacteriophage were constructed as templates for mini-mRNA synthesis. Two strategies were used to introduce photo-reactive agents into the message. According to the first, two transcripts were isolated from E coli and chemically derivatized at their 5'-ends with a photoinducible diaziril group. One of these messages allowed for localization of the 5'-end of the Shine-Dalgarno sequence while the other one allowed for labeling of the ribosome at the 5'-end side of the initiation AUG codon in the P site. According to the second approach, 5-azidouridine (5N3U) was randomly incorporated into mRNA transcripts during a T7 RNA polymerase catalyzed reaction by using a mixture of 5N3UTP and UTP. A message that had U residues at either -4, -3, -1, +2 and +14, +19, +20 positions was used (A from cro AUG is +1). Whereas cross-links with the 5N3U transcripts were essentially 'zero-length', the 5'-derivatized transcripts were covalently attached to ribosomal components about 14 A from the 5'-end. We found that proteins S1, S7, S5, S3 and S4 compose, or were close to, the ribosomal mRNA-binding site.(ABSTRACT TRUNCATED AT 250 WORDS)