Mechanisms regulating the secretion of the promalignancy chemokine CCL5 by breast tumor cells: CCL5's 40s loop and intracellular glycosaminoglycans

The Recruitment of Neutrophils to the Tumor Microenvironment Is Regulated by Multiple Mediators

Neutrophils sense and migrate towards chemotactic factors released at sites of infection/inflammation and contain the affected area using a variety of effector mechanisms. Aside from these established immune defense functions, neutrophils are emerging as one of the key tumor-infiltrating immune cells that influence cancer progression and metastasis. Neutrophil recruitment to the tumor microenvironment (TME) is mediated by multiple mediators including cytokines, chemokines, lipids, and growth factors that are secreted from cancer cells and cancer-associated stromal cells. However, the molecular mechanisms that underlie the expression and secretion of the different mediators from cancer cells and how neutrophils integrate these signals to reach and invade tumors remain unclear. Here, we discuss the possible role of the epithelial to mesenchymal transition (EMT) program, which is a well-established promoter of malignant potential in cancer, in regulating the expression and secretion of these key mediators. We also summarize and review our current understanding of the machineries that potentially control the secretion of the mediators from cancer cells, including the exocytic trafficking pathways, secretory autophagy, and extracellular vesicle-mediated secretion. We further reflect on possible mechanisms by which different mediators collaborate by integrating their signaling network, and particularly focus on TGF-β, a cytokine that is highly expressed in invasive tumors, and CXCR2 ligands, which are crucial neutrophil recruiting chemokines. Finally, we highlight gaps in the field and the need to expand current knowledge of the secretory machineries and cross-talks among mediators to develop novel neutrophil targeting strategies as effective therapeutic options in the treatment of cancer.

Chemokines and their Receptors: Multifaceted Roles in Cancer Progression and Potential Value as Cancer Prognostic Markers

Chemokines are chemotactic cytokines that mediate immune cell chemotaxis and lymphoid tissue development. Recent advances have indicated that chemokines and their cognate receptors play critical roles in cancer-related inflammation and cancer progression. On the basis of these findings, the chemokine system has become a new potential drug target for cancer immunotherapy. In this review, we summarize the essential roles of the complex network of chemokines and their receptors in cancer progression. Furthermore, we discuss the potential value of the chemokine system as a cancer prognostic marker. The chemokine system regulates the infiltration of immune cells into the tumor microenvironment, which induces both pro- and anti-immunity and promotes or suppresses tumor growth and proliferation, angiogenesis, and metastasis. Increasing evidence indicates the promising prognostic value of the chemokine system in cancer patients. While CCL2, CXCL10, and CX3CL1/CX3CR1 can serve as favorable or unfavorable prognostic factors depending on the cancer types, CCL14 and XCL1 possess good prognostic value. Other chemokines such as CXCL1, CXCL8, and CXCL12 are poor prognostic markers. Despite vast advances in our understanding of the complex nature of the chemokine system in tumor biology, knowledge about the multifaceted roles of the chemokine system in different types of cancers is still limited. Further studies are necessary to decipher distinct roles within the chemokine system in terms of cancer progression and to validate their potential value in cancer prognosis.

Identification of CCL5/RANTES as a novel contraction-reducible myokine in mouse skeletal muscle

Skeletal muscle is an endocrine organ that secretes several proteins, which are collectively termed myokines. Although many studies suggest that exercise regulates myokine secretion, the underlying mechanisms remain unclear and all the exercise-dependent myokines have not yet been identified. Therefore, in this study, we attempted to identify novel exercise-dependent myokines by using our recently developed in vitro contractile model. Differentiated C2C12 myotubes were cultured with or without electrical pulse stimulation (EPS) for 24 h to induce cell contraction, and the myokines secreted in conditioned medium were analyzed using a cytokine array. Although most myokine secretions were not affected by EPS, the secretion of Chemokine (C-C motif) ligand 5 (CCL5) (regulated on activation, normal T cell expressed and secreted (RANTES)) was significantly reduced by EPS. This was further confirmed by ELISA and quantitative PCR. Contraction-dependent calcium transients and activation of 5'-AMP activating protein kinase (AMPK) appears to be involved in this decrease, as the chelating Ca²⁺ by EGTA blocked contraction-dependent CCL5 reduction, whereas the pharmacological activation of AMPK significantly reduced it. However, Ccl5 gene expression was increased by AMPK activation, suggesting that AMPK-dependent CCL5 decrease occurred via post-transcriptional regulation. Finally, mouse experiments revealed that voluntary wheel-running exercise reduced serum CCL5 levels and Ccl5 gene expression in the fast-twitch muscles. Overall, our study provides the first evidence of an exercise-reducible myokine, CCL5, in the mouse skeletal muscle. Although further studies are required to understand the precise roles of the skeletal muscle cell contraction-induced decrease in CCL5, this decrease may explain some exercise-dependent physiological changes such as those in immune responses.

Targeting autophagy inhibits melanoma growth by enhancing NK cells infiltration in a CCL5-dependent manner

The failure in achieving a durable clinical immune response against cancer cells depends on the ability of cancer cells to establish a microenvironment that prevent cytotoxic immune cells to infiltrate tumors and kill cancer cells. Therefore, the key approach to achieving successful antitumor immune response is to harness strategies allowing the reorientation of immune cells to the tumor. Herein we reveal that inhibiting autophagy induces a massive infiltration of natural killer immune cells into the tumor bed, and a subsequent dramatic decrease in the tumor volume of melanomas. These results highlight the role of targeting autophagy in breaking the immunosuppressive tumor microenvironment barrier, thus allowing the infiltration of natural killer cells into the tumor to kill cancer cells.

While blocking tumor growth by targeting autophagy is well established, its role on the infiltration of natural killer (NK) cells into tumors remains unknown. Here, we investigate the impact of targeting autophagy gene Beclin1 (BECN1) on the infiltration of NK cells into melanomas. We show that, in addition to inhibiting tumor growth, targeting BECN1 increased the infiltration of functional NK cells into melanoma tumors. We provide evidence that driving NK cells to the tumor bed relied on the ability of autophagy-defective tumors to transcriptionally overexpress the chemokine gene CCL5. Such infiltration and tumor regression were abrogated by silencing CCL5 in BECN1-defective tumors. Mechanistically, we show that the up-regulated expression of CCL5 occurred through the activation of its transcription factor c-Jun by a mechanism involving the impairment of phosphatase PP2A catalytic activity and the subsequent activation of JNK. Similar to BECN1, targeting other autophagy genes, such as ATG5, p62/SQSTM1, or inhibiting autophagy pharmacologically by chloroquine, also induced the expression of CCL5 in melanoma cells. Clinically, a positive correlation between CCL5 and NK cell marker NKp46 expression was found in melanoma patients, and a high expression level of CCL5 was correlated with a significant improvement of melanoma patients’ survival. We believe that this study highlights the impact of targeting autophagy on the tumor infiltration by NK cells and its benefit as a novel therapeutic approach to improve NK-based immunotherapy.

Two glycosaminoglycan-binding domains of the mouse cytomegalovirus-encoded chemokine MCK-2 are critical for oligomerization of the full-length protein

Chemokines are essential for antimicrobial host defenses and tissue repair. Herpesviruses and poxviruses also encode chemokines, copied from their hosts and repurposed for multiple functions, including immune evasion. The CC chemokine MCK-2 encoded by mouse CMV (MCMV) has an atypical structure consisting of a classic chemokine domain N-terminal to a second unique domain, resulting from the splicing of MCMV ORFs m131 and m129 MCK-2 is essential for full MCMV infectivity in macrophages and for persistent infection in the salivary gland. However, information about its mechanism of action and specific biochemical roles for the two domains has been lacking. Here, using genetic, chemical, and enzymatic analyses of multiple mouse cell lines as well as primary mouse fibroblasts from salivary gland and lung, we demonstrate that MCK-2 binds glycosaminoglycans (GAGs) with affinities in the following order: heparin > heparan sulfate > chondroitin sulfate = dermatan sulfate. Both MCK-2 domains bound these GAGs independently, and computational analysis together with site-directed mutagenesis identified five basic residues distributed across the N terminus and the 30s and 50s loops of the chemokine domain that are important GAG binding determinants. Both domains were required for GAG-dependent oligomerization of full-length MCK-2. Thus, MCK-2 is an atypical viral chemokine consisting of a CC chemokine domain and a unique non-chemokine domain, both of which bind GAGs and are critical for GAG-dependent oligomerization of the full-length protein.

Criteria derived from serum markers can precisely evaluate axillary status in breast cancer patients

BACKGROUND

A noninvasive method to confirm the presence of lymph node metastases (LNM) in breast cancer patients is lacking. This study aimed to identify markers from peripheral blood that have diagnostic value in evaluating axillary LNM.

METHODS

We tested 26 factors in serum from 57 patients with resectable breast cancer by the Luminex assay. Differences between node-negative and node-positive patients were assessed. The diagnostic value of the factors was determined by further analyses and a validation test.

RESULTS

Matrix metalloproteinase-1, hepatocyte growth factor, and chemokine ligand 5 were independent risk factors for LNM. However, receiver operating characteristic analysis showed that these factors alone were not ideal predictors. The LNM score (LNMS), derived from combining these markers, correlated significantly with numbers of positive lymph nodes. Patients with LNMS of 0 had few LNM, axillary lymph node dissection (ALND) could be avoided, and sentinel lymph node biopsy (SLNB) was unnecessary. Very high accuracy was achieved for patients with LNMS of 1 with SLNB using only methylene blue, patients with LNMS of 3 required ALND, and patients with LNMS of 2 needed SLNB using both a radioactive isotope and methylene blue, and ALND.

CONCLUSIONS

The LNMS derived from matrix metalloproteinase-1, hepatocyte growth factor, and chemokine ligand 5 serum levels identified the axillary lymph node status with high accuracy. Patients with higher LNMS had a greater probability of LNM.

The dependence of chemokine-glycosaminoglycan interactions on chemokine oligomerization

Both chemokine oligomerization and binding to glycosaminoglycans (GAGs) are required for their function in cell recruitment. Interactions with GAGs facilitate the formation of chemokine gradients, which provide directional cues for migrating cells. In contrast, chemokine oligomerization is thought to contribute to the affinity of GAG interactions by providing a more extensive binding surface than single subunits alone. However, the importance of chemokine oligomerization to GAG binding has not been extensively quantified. Additionally, the ability of chemokines to form different oligomers has been suggested to impart specificity to GAG interactions, but most studies have been limited to heparin. In this study, several differentially oligomerizing chemokines (CCL2, CCL3, CCL5, CCL7, CXCL4, CXCL8, CXCL11 and CXCL12) and select oligomerization-deficient mutants were systematically characterized by surface plasmon resonance to determine their relative affinities for heparin, heparan sulfate (HS) and chondroitin sulfate-A (CS-A). Wild-type chemokines demonstrated a hierarchy of binding affinities for heparin and HS that was markedly dependent on oligomerization. These results were corroborated by their relative propensity to accumulate on cells and the critical role of oligomerization in cell presentation. CS-A was found to exhibit greater chemokine selectivity than heparin or HS, as it only bound a subset of chemokines; moreover, binding to CS-A was ablated with oligomerization-deficient mutants. Overall, this study definitively demonstrates the importance of oligomerization for chemokine-GAG interactions, and demonstrates diversity in the affinity and specificity of different chemokines for GAGs. These data support the idea that GAG interactions provide a mechanism for fine-tuning chemokine function.

Breast cancer: coordinated regulation of CCL2 secretion by intracellular glycosaminoglycans and chemokine motifs

The chemokine CCL2 (MCP-1) has been identified as a prominent tumor-promoting factor in breast cancer. The major source for CCL2 is in the tumor cells; thus, identifying the mechanisms regulating CCL2 release by these cells may enable the future design of modalities inhibiting CCL2 secretion and consequently reduce tumorigenicity. Using cells deficient in expression of glycosaminoglycans (GAGs) and short hairpin RNAs reducing heparan sulfate (HS) and chondroitin sulfate (CS) expression, we found that intracellular HS and CS (= GAGs) partly controlled the trafficking of CCL2 from the Golgi toward secretion. Next, we determined the secretion levels of GFP-CCL2-WT and GFP-CCL2-variants mutated in GAG-binding domains and/or in the 40s loop of CCL2 (⁴⁵TIVA⁴⁸). We have identified partial roles for R18+K19, H66, and the ⁴⁵TIVA⁴⁸ motif in regulating CCL2 secretion. We have also demonstrated that in the absence of R24 or R18+K19 +⁴⁵TIVA⁴⁸, the secretion of CCL2 by breast tumor cells was almost abolished. Analyses of the intracellular localization of GFP-CCL2-mutants in the Golgi or the endoplasmic reticulum revealed particular intracellular processes in which these CCL2 sequences controlled its intracellular trafficking and secretion. The R24, ⁴⁵TIVA⁴⁸ and R18+K19 +⁴⁵TIVA⁴⁸ domains controlled CCL2 secretion also in other cell types. We propose that targeting these chemokine regions may lead to reduced secretion of CCL2 by breast cancer cells (and potentially also by other malignant cells). Such a modality may limit tumor growth and metastasis, presumably without affecting general immune activities (as discussed below).

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

Multiple glycosaminoglycan-binding epitopes of monocyte chemoattractant protein-3/CCL7 enable it to function as a non-oligomerizing chemokine

The interaction of chemokines with glycosaminoglycans (GAGs) facilitates the formation of localized chemokine gradients that provide directional signals for migrating cells. In this study, we set out to understand the structural basis and impact of the differing oligomerization propensities of the chemokines monocyte chemoattractant protein (MCP)-1/CCL2 and MCP-3/CCL7 on their ability to bind GAGs. These chemokines provide a unique comparison set because CCL2 oligomerizes and oligomerization is required for its full in vivo activity, whereas CCL7 functions as a monomer. To identify the GAG-binding determinants of CCL7, an unbiased hydroxyl radical footprinting approach was employed, followed by a focused mutagenesis study. Compared with the size of the previously defined GAG-binding epitope of CCL2, CCL7 has a larger binding site, consisting of multiple epitopes distributed along its surface. Furthermore, surface plasmon resonance (SPR) studies indicate that CCL7 is able to bind GAGs with an affinity similar to CCL2 but higher than the non-oligomerizing variant, CCL2(P8A), suggesting that, in contrast to CCL2, the large cluster of GAG-binding residues in CCL7 renders oligomerization unnecessary for high affinity binding. However, the affinity of CCL7 is more sensitive than CCL2 to the density of heparan sulfate on the SPR surfaces; this is likely due to the inability of CCL7 to oligomerize because CCL2(P8A) also binds significantly less tightly to low than high density heparan sulfate surfaces compared with CCL2. Together, the data suggest that CCL7 and CCL2 are non-redundant chemokines and that GAG chain density may provide a mechanism for regulating the accumulation of chemokines on cell surfaces.

The chemokine CCL5 induces CCR1-mediated hyperalgesia in mice inoculated with NCTC 2472 tumoral cells

Although the expression of the chemokine receptor CCR1 has been demonstrated in several structures related to nociception, supporting the nociceptive role of chemokines able to activate it, the involvement of CCR1 in neoplastic pain has not been previously assessed. We have assayed the effects of a CCR1 antagonist, J113863, in two murine models of neoplastic hyperalgesia based on the intratibial injection of either NCTC 2472 fibrosarcoma cells, able to induce osteolytic bone injury, or B16-F10 melanoma cells, associated to mixed osteolytic/osteoblastic bone pathological features. The systemic administration of J113863 inhibited thermal and mechanical hyperalgesia but not mechanical allodynia in mice inoculated with NCTC 2472 cells. Moreover, in these mice, thermal hyperalgesia was counteracted following the peritumoral (10-30μg) but not spinal (3-5μg) administration of J113863. In contrast, hyperalgesia and allodynia measured in mice inoculated with B16-F10 cells remained unaffected after the administration of J113863. The inoculation of tumoral cells did not modify the levels of CCL3 at tumor or spinal cord. In contrast, although the concentration of CCL5 remained unmodified in mice inoculated with B16-F10 cells, increased levels of this chemokine were measured in tumor-bearing limbs, but not the spinal cord, of mice inoculated with NCTC 2472 cells. Increased levels of CCL5 were also found following the incubation of NCTC 2472, but not B16-F10, cells in the corresponding culture medium. The intraplantar injection of CCL5 (0.5ng) to naïve mice evoked thermal hyperalgesia prevented by the coadministration of J113863 or the CCR5 antagonist, d-Ala-peptide T-amide (DAPTA), demonstrating that CCL5 can induce thermal hyperalgesia in mice through the activation of CCR1 or CCR5. However, contrasting with the inhibitory effect evoked by J113863, the systemic administration of DAPTA did not prevent tumoral hyperalgesia. Finally, the peritumoral administration of an anti-CCL5 antibody completely inhibited thermal hyperalgesia evoked by the inoculation of NCTC 2472 cells.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.