Chemerin partly mediates tumor-inhibitory effect of all-trans retinoic acid via CMKLR1-dependent natural killer cell recruitment.

Down-regulated chemerin expression has been reported to correlate with poor prognosis of several types of cancer including melanoma. All-trans retinoic acid (atRA) is a potent inducer of chemerin, and we previously reported that atRA inhibited murine melanoma growth through enhancement of anti-tumor T-cell immunity. Here, we aimed to investigate whether loss of endogenous chemerin accelerated melanoma growth and whether chemerin was involved in the melanoma-inhibitory effect of atRA. We demonstrated that chemerin was constitutively expressed in the skin, which was down-regulated during murine melanoma growth. Rarres2-/- mice, which are deficient in chemerin, exhibited aggravated tumor growth and impaired tumor-infiltrating natural killer (NK) cells that express CMKLR1, the functional receptor of chemerin. Topical treatment with atRA up-regulated skin chemerin expression, which was primarily derived from dermal cells. Moreover, atRA treatment significantly enhanced tumor-infiltrating NK cells, which was completely abrogated in Rarres2-/- mice and Cmklr1-/- mice, suggesting a dependency of NK cell recruitment on the chemerin-CMKLR1 axis in melanoma. Despite comparable melanoma growth detected in wild-type mice and Cmklr1-/- mice, lack of CMKLR1 partially abrogated the melanoma-inhibitory effect of atRA. This may be due to the inability to enhance tumor-infiltrating NK cells in Cmklr1-/- mice following atRA treatment. Collectively, our study suggests that down-regulation of chemerin could be a strategy used by cancers such as melanoma to impair anti-tumor NK cell immunity and identifies a new anti-tumor mechanism of atRA by up-regulating chemerin to enhance CMKLR1-dependent NK cell recruitment.

Song Y ，Yin W ，Dan Y ，Sheng J ，Zeng Y ，He R ... -  《-》

The chemoattractant chemerin suppresses melanoma by recruiting natural killer cell antitumor defenses.

Pachynski RK ，Zabel BA ，Kohrt HE ，Tejeda NM ，Monnier J ，Swanson CD ，Holzer AK ，Gentles AJ ，Sperinde GV ，Edalati A ，Hadeiba HA ，Alizadeh AA ，Butcher EC ... -  《-》

Topical treatment of all-trans retinoic acid inhibits murine melanoma partly by promoting CD8(+) T-cell immunity.

All-trans retinoic acid (atRA), the main biologically active metabolite of vitamin A, has been implicated in immunoregulation and anti-cancer. A recent finding that vitamin A could decrease the risk of melanoma in humans indicates the beneficial role of atRA in melanoma. However, it remains unknown whether topical application of atRA could inhibit melanoma growth by influencing tumour immunity. We demonstrate topical application of tretinoin ointment (atRA as the active ingredient) effectively inhibited B16F10 melanoma growth. This is accompanied by markedly enhanced CD8+ T-cell responses, as evidenced by significantly increased proportions of effector CD8+ T cells expressing granzyme B, tumour necrosis factor-α, or interferon-γ, and Ki67+ proliferating CD8+ T cells in atRA-treated tumours compared with vaseline controls. Furthermore, topical atRA treatment promoted the differentiation of effector CD8+ T cells in draining lymph nodes (DLN) of tumour-bearing mice. Interestingly, atRA did not affect tumoral CD4+ T-cell response, and even inhibited the differentiation of interferon-γ-expressing T helper type 1 cells in DLN. Importantly, we demonstrated that the tumour-inhibitory effect of atRA was partly dependent on CD8+ T cells, as CD8+ T-cell depletion restored tumour volumes in atRA-treated mice, which, however, was still significantly smaller than those in vaseline-treated mice. Finally, we demonstrated that atRA up-regulated MHCI expression in B16F10 cells, and DLN cells from tumour-bearing mice had a significantly higher killing rate when culturing with atRA-treated B16F10 cells. Hence, our study demonstrates that topical atRA treatment effectively inhibits melanoma growth partly by promoting the differentiation and the cytotoxic function of effector CD8+ T cells.

Yin W ，Song Y ，Liu Q ，Wu Y ，He R ... -  《-》

Chemerin triggers migration of a CD8 T cell subset with natural killer cell functions.

The recruitment of cells with effector functions into the tumor microenvironment holds potential for delaying cancer progression. We show that subsets of human CD28-effector CD8 T cells, CCR7- CD45RO+ effector memory, and CCR7- CD45RO- effector memory RA phenotypes, express the chemerin receptor CMKLR1 and bind chemerin via the receptor. CMKLR1-expressing human CD8 effector memory T cells present gene, protein, and cytotoxic features of NK cells. Active chemerin promotes chemotaxis of CMKLR1-expressing CD8 effector memory cells and triggers activation of the α4β1 integrin. In an experimental prostate tumor mouse model, chemerin expression is downregulated in the tumor microenvironment, which is associated with few tumor-infiltrating CD8+ T cells, while forced overexpression of chemerin by mouse prostate cancer cells leads to an accumulation of intra-tumor CD8+ T cells. Furthermore, α4 integrin blockade abrogated the chemerin-dependent recruitment of CD8+ T effector memory cells into implanted prostate tumors in vivo. The results identify a role for chemerin:CMKLR1 in defining a specialized NK-like CD8 T cell, and suggest the use of chemerin-dependent modalities to target effector CMKLR1-expressing T cells to the tumor microenvironment for immunotherapeutic purposes.

Ballet R ，LaJevic M ，Huskey-Mullin N ，Roach R ，Brulois K ，Huang Y ，Saeed MA ，Dang HX ，Pachynski RK ，Wilson E ，Butcher EC ，Zabel BA ... -  《-》

Chemerin-activated functions of CMKLR1 are regulated by G protein-coupled receptor kinase 6 (GRK6) and β-arrestin 2 in inflammatory macrophages.

Chemerin receptor (CMKLR1) is a G protein-coupled receptor (GPCR) implicated in macrophage-mediated inflammation and in several forms of human arthritis. Analogous to other GPCR, CMKLR1 is likely regulated by G protein-coupled receptor kinase (GRK) phosphorylation of intracellular domains in an activation-dependent manner, which leads to recruitment and termination of intracellular signaling via desensitization and internalization of the receptor. The ubiquitously expressed GRK family members include GRK2, GRK3, GRK5, and GRK6, but it is unknown which GRK regulates CMKLR1 cellular and signaling functions. Our data show that activation of CMKLR1 by chemerin in primary macrophages leads to signaling and functional outcomes that are regulated by GRK6 and β-arrestin 2. We show that arrestin recruitment to CMKLR1 following chemerin stimulation is enhanced with co-expression of GRK6. Further, internalization of endogenous CMKLR1, following the addition of chemerin, is decreased in inflammatory macrophages from GRK6- and β-arrestin 2-deficient mice. These GRK6- and β-arrestin 2-deficient macrophages display increased migration toward chemerin and altered AKT and Extracellular-signal Related Kinase (ERK) signaling. Our findings show that chemerin-activated CMKLR1 regulation in inflammatory macrophages is largely GRK6 and β-arrestin mediated, which may impact innate immunity and have therapeutic implications in rheumatic disease.

Serafin DS ，Allyn B ，Sassano MF ，Timoshchenko RG ，Mattox D ，Brozowski JM ，Siderovski DP ，Truong YK ，Esserman D ，Tarrant TK ，Billard MJ ... -  《-》