Affinity-matured homotypic interactions induce spectrum of PfCSP structures that influence protection from malaria infection

The generation of high-quality antibody responses to Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP), the primary surface antigen of Pf sporozoites, is paramount to the development of an effective malaria vaccine. Here we present an in-depth structural and functional analysis of a panel of potent antibodies encoded by the immunoglobulin heavy chain variable (IGHV) gene IGHV3-33, which is among the most prevalent and potent antibody families induced in the anti-PfCSP immune response and targets the Asn-Ala-Asn-Pro (NANP) repeat region. Cryo-electron microscopy (cryo-EM) reveals a remarkable spectrum of helical antibody-PfCSP structures stabilized by homotypic interactions between tightly packed fragments antigen binding (Fabs), many of which correlate with somatic hypermutation. We demonstrate a key role of these mutated homotypic contacts for high avidity binding to PfCSP and in protection from Pf malaria infection. Together, these data emphasize the importance of anti-homotypic affinity maturation in the frequent selection of IGHV3-33 antibodies and highlight key features underlying the potent protection of this antibody family.

Activation of a Latent Epitope Causing Differential Binding of Antineutrophil Cytoplasmic Antibodies to Proteinase 3

OBJECTIVE

Proteinase 3 (PR3) is the major antigen for antineutrophil cytoplasmic antibodies (ANCAs) in the systemic autoimmune vasculitis, granulomatosis with polyangiitis (GPA). PR3-targeting ANCAs (PR3-ANCAs) recognize different epitopes on PR3. This study was undertaken to study the effect of mutations on PR3 antigenicity.

METHODS

The recombinant PR3 variants, iPR3 (clinically used to detect PR3-ANCAs) and iHm5 (containing 3 point mutations in epitopes 1 and 5 generated for epitope mapping studies) immunoassays and serum samples from patients enrolled in ANCA-associated vasculitis (AAV) trials were used to screen for differential PR3-ANCA binding. A patient-derived monoclonal ANCA 518 (moANCA518) that selectively binds to iHm5 within the mutation-free epitope 3 and is distant from the point mutations of iHm5 was used as a gauge for remote epitope activation. Selective binding was determined using inhibition experiments.

RESULTS

Rather than reduced binding of PR3-ANCAs to iHm5, we found substantially increased binding of the majority of PR3-ANCAs to iHm5 compared to iPR3. This differential binding of PR3-ANCA to iHm5 is similar to the selective moANCA518 binding to iHm5. Binding of iPR3 to monoclonal antibody MCPR3-2 also induced recognition by moANCA518.

CONCLUSION

The preferential binding of PR3-ANCAs from patients, such as the selective binding of moANCA518 to iHm5, is conferred by increased antigenicity of epitope 3 on iHm5. This can also be induced on iPR3 when captured by monoclonal antibody MCPR2. This previously unrecognized characteristic of PR3-ANCA interactions with its target antigen has implications for studying antibody-mediated autoimmune diseases, understanding variable performance characteristics of immunoassays, and design of potential novel treatment approaches.

A novel CSP C-terminal epitope targeted by an antibody with protective activity against Plasmodium falciparum

Potent and durable vaccine responses will be required for control of malaria caused by Plasmodium falciparum (Pf). RTS,S/AS01 is the first, and to date, the only vaccine that has demonstrated significant reduction of clinical and severe malaria in endemic cohorts in Phase 3 trials. Although the vaccine is protective, efficacy declines over time with kinetics paralleling the decline in antibody responses to the Pf circumsporozoite protein (PfCSP). Although most attention has focused on antibodies to repeat motifs on PfCSP, antibodies to other regions may play a role in protection. Here, we expressed and characterized seven monoclonal antibodies to the C-terminal domain of CSP (ctCSP) from volunteers immunized with RTS,S/AS01. Competition and crystal structure studies indicated that the antibodies target two different sites on opposite faces of ctCSP. One site contains a polymorphic region (denoted α-ctCSP) and has been previously characterized, whereas the second is a previously undescribed site on the conserved β-sheet face of the ctCSP (denoted β-ctCSP). Antibodies to the β-ctCSP site exhibited broad reactivity with a diverse panel of ctCSP peptides whose sequences were derived from field isolates of P. falciparum whereas antibodies to the α-ctCSP site showed very limited cross reactivity. Importantly, an antibody to the β-site demonstrated inhibition activity against malaria infection in a murine model. This study identifies a previously unidentified conserved epitope on CSP that could be targeted by prophylactic antibodies and exploited in structure-based vaccine design.

Abstract CT203: First-in-human phase 1b study of ATRC-101, a patient-derived antibody with a tumor-specific target, as monotherapy or in combination with pembrolizumab, in patients with solid tumors

Background: ATRC-101 is a fully human, engineered IgG1 version of an antibody discovered through a target-agnostic process designed to identify patient-derived, tumor-targeting antibodies. The parental antibody of ATRC-101 was discovered from a patient with metastatic non-small cell lung cancer (NSCLC) undergoing an active immune response while receiving a checkpoint inhibitor. ATRC-101 binds selectively to human tumor specimens, including a majority of NSCLC, acral melanoma, breast, colorectal, and ovarian cancer samples. The target of ATRC-101 appears to be a tumor-associated ribonucleoprotein complex containing a form of polyadenylate-binding protein 1 (PABP-1) that can be found on the surface of tumor cells. Studies to further elucidate the tumor selectivity of ATRC-101 and the extracellular presentation of the target are ongoing. Preclinical data suggest that ATRC-101 stimulates an adaptive immune response against tumors via the innate immune system. ATRC-101 displays dose-dependent, single-agent activity in syngeneic mouse tumor models, including the EMT6 breast cancer model, which displays a T cell-excluded microenvironment and in which PD-1/PD-L1 inhibitors exhibit limited activity. ATRC-101 plus an anti-PD-1 antibody demonstrated significantly greater antitumor activity and longer survival in the EMT6 model compared with either agent alone, consistent with the mechanism of action proposed for ATRC-101. Methods: ATRC-101-A01 is an open-label, 3+3, dose-escalation phase 1b safety study of ATRC-101 as monotherapy (mono) or in combination (combo) with pembrolizumab (pembro) to treat patients with certain solid tumor types. Expansion cohorts of ≤12 patients may be enrolled at doses and frequencies at which biological activity is observed. The primary objective is to determine the safety of ATRC-101. Secondary objectives include evaluation of the following: recommended dose and schedule of ATRC-101 for expansion, pharmacokinetic profile of ATRC-101, immunogenicity, antitumor activity by RECIST v1.1, and lymphocytic infiltration in the tumor microenvironment. ATRC-101 is administered every 2 (q2w) or 3 (q3w) weeks up to 24 months or until disease progression. ATRC-101 dosing is increasing from the initial 0.3 mg/kg according to the following schedule, pending dose-limiting toxicity data: 1, 3, 10, and 30 mg/kg. In the combo cohort, ATRC-101 will be given q3w, and pembro will be administered at 200 mg q3w or 400 mg q6w to patients with disease progression while receiving prior pembro treatment or those with stable disease who were deemed by their physician to potentially benefit from the addition of ATRC-101. The q3w mono cohort is currently accruing patients at the 10-mg/kg dose, and the combo and q2w cohorts will begin at an ATRC-101 dose one level below the most recent cleared q3w mono dose. Trial registration NCT04244552. The study was approved by the institutional review board of each participating site.

Citation Format: Jonathan E. Benjamin, Nicholas Higgins, Carl Millward, Jeff DeFalco, Amy Manning-Bog, Iraz T. Aydin, Danhui Zhang, Shaun M. Lippow, Alexander Scholz, Yvonne Leung, Yanhong Zhu, Anna Sedello, Zane Rogers, Ish K. Dhawan, Daniel Emerling, William H. Robinson, Tito A. Serafini, Norman M. Greenberg. First-in-human phase 1b study of ATRC-101, a patient-derived antibody with a tumor-specific target, as monotherapy or in combination with pembrolizumab, in patients with solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT203.

Structural and biophysical correlation of anti-NANP antibodies with in vivo protection against P. falciparum

The most advanced P. falciparum circumsporozoite protein-based malaria vaccine, RTS,S/AS01 (RTS,S), confers partial protection but with antibody titers that wane relatively rapidly, highlighting the need to elicit more potent and durable antibody responses. Here, we elucidate crystal structures, binding affinities and kinetics, and in vivo protection of eight anti-NANP antibodies derived from an RTS,S phase 2a trial and encoded by three different heavy-chain germline genes. The structures reinforce the importance of homotypic Fab-Fab interactions in protective antibodies and the overwhelmingly dominant preference for a germline-encoded aromatic residue for recognition of the NANP motif. In this study, antibody apparent affinity correlates best with protection in an in vivo mouse model, with the more potent antibodies also recognizing epitopes with repeating secondary structural motifs of type I β- and Asn pseudo 310 turns; such insights can be incorporated into design of more effective immunogens and antibodies for passive immunization.

First-in-human phase Ib study of ATRC-101, an engineered version of a patient-derived antibody targeting a tumor-restricted ribonucleoprotein complex

TPS3168

Background: ATRC-101 is a fully human, engineered IgG1 version of an antibody discovered through a a target-agnostic screen to identify patient-derived antibodies that bind selectively to public tumor antigens. The parental antibody was identified from B cells in the active immune response of a patient receiving checkpoint therapy for Stage IV non-small cell lung cancer (NSCLC). A fluorescently conjugated version of ATRC-101 binds selectively to human tumor specimens including a majority of NSCLC, acral melanoma, breast, colorectal, and ovarian cancer samples. No reactivity of toxicological significance is found across a wide range of normal human tissues. ATRC-101 displays dose-dependent, single-agent activity in syngeneic mouse tumor models, including the EMT6 breast cancer model, which displays a T cell-excluded microenvironment often observed in human tumors, and in which checkpoint inhibitors targeting the PD-1 axis exhibit limited activity. Dosing with ATRC-101 in the EMT6 model causes marked changes in the tumor microenvironment, including a shift from the M2 to the M1 macrophage phenotype and infiltration of T cells. ATRC-101 does not appear to act via NK cell-driven ADCC; instead, activity in vivo is dependent both on Fc region interactions with Fc receptors, likely on myeloid rather than lymphoid cells, and on the presence of CD8+ T cells. ATRC-101 binds to a target that is a ribonucleoprotein (RNP) complex containing polyadenylate-binding protein 1 (PABP-1) bound to poly(A)RNA. Whereas both PABP-1 and poly(A)RNA are ubiquitously expressed at high levels in normal tissues and have been localized intracellularly, the ATRC-101 target is detected extracellularly on tumor cells grown in vivo. The basis for the tumor-selectivity of ATRC-101 as well as the extracellular localization of the target is under investigation. Ascending doses of ATRC-101 were well tolerated in multiple non-clinical safety studies. Methods: ATRC-101-A01 is an open-label, 3+3, Phase 1b safety study in patients with acral melanoma, NSCLC, breast, ovarian, and colorectal cancers. Participants are accruing in the first dose cohort. ATRC-101 is administered every 21 days up to 24 months or until disease progression. The primary objective of the trial is to determine the safety and tolerability of ATRC-101. Secondary objectives are to characterize the pharmacokinetic profiles of ATRC-101 and to assess antitumor activity as determined by RECIST 1.1 and lymphocytic infiltration in the tumor microenvironment. Clinical trial information: NCT04244552 .

Structure and mechanism of monoclonal antibody binding to the junctional epitope of Plasmodium falciparum circumsporozoite protein

Lasting protection has long been a goal for malaria vaccines. The major surface antigen on Plasmodium falciparum sporozoites, the circumsporozoite protein (PfCSP), has been an attractive target for vaccine development and most protective antibodies studied to date interact with the central NANP repeat region of PfCSP. However, it remains unclear what structural and functional characteristics correlate with better protection by one antibody over another. Binding to the junctional region between the N-terminal domain and central NANP repeats has been proposed to result in superior protection: this region initiates with the only NPDP sequence followed immediately by NANP. Here, we isolated antibodies in Kymab mice immunized with full-length recombinant PfCSP and two protective antibodies were selected for further study with reactivity against the junctional region. X-ray and EM structures of two monoclonal antibodies, mAb667 and mAb668, shed light on their differential affinity and specificity for the junctional region. Importantly, these antibodies also bind to the NANP repeat region with equal or better affinity. A comparison with an NANP-only binding antibody (mAb317) revealed roughly similar but statistically distinct levels of protection against sporozoite challenge in mouse liver burden models, suggesting that junctional antibody protection might relate to the ability to also cross-react with the NANP repeat region. Our findings indicate that additional efforts are necessary to isolate a true junctional antibody with no or much reduced affinity to the NANP region to elucidate the role of the junctional epitope in protection.

The circumsporozoite protein (CSP) of Plasmodium falciparum malaria has been the foundation for the design of transmission blocking malaria vaccines. To date, the most promising CSP-based vaccine candidate is RTS,S, which consists of the central repeating NANP amino-acid sequence and the C-terminal domain of CSP fused to hepatitis B surface antigen that assembles into virus-like particles. Potential shortcomings of RTS,S includes the lack of other potential CSP epitopes such as the junctional epitope, which is located between the N-terminal domain of CSP and the start of the NANP repeat region. Here, we elicited antibodies against full-length CSP and screened for junctional epitope binding. We then used an array of biophysical techniques to elucidate the nature of the binding and tested the level of two protective antibodies in a mouse challenge model. Although the antibodies were able to bind both junctional and NANP epitopes, the in vivo data showed distinct levels of protection between themselves and also to an NANP-only binder. Our data suggest that their protection ability may be related to the strong cross-reactivity with NANP epitopes. Since all reported junctional antibodies to date have dual-specificity, we suggest that a true junctional binder with no or very low NANP affinity, if one can be found, is essential to evaluate the contribution of the junctional epitope to protection.

Diverse Antibody Responses to Conserved Structural Motifs in Plasmodium falciparum Circumsporozoite Protein

Malaria vaccine candidate RTS,S/AS01 is based on the central and C-terminal regions of the circumsporozoite protein (CSP) of P. falciparum. mAb397 was isolated from a volunteer in an RTS,S/AS01 clinical trial, and it protects mice from infection by malaria sporozoites. However, mAb397 originates from the less commonly used VH3-15 germline gene compared to the VH3-30/33 antibodies generally elicited by RTS,S to the central NANP repeat region of CSP. The crystal structure of mAb397 with an NPNA₄ peptide shows that the central NPNA forms a type I β-turn and is the main recognition motif. In most anti-NANP antibodies studied to date, a germline-encoded Trp is used to engage the Pro in NPNA β-turns, but here the Trp interacts with the first Asn. This “conserved” Trp, however, can arise from different germline genes and be located in the heavy or the light chain. Variation in the terminal ψ angles of the NPNA β-turns results in different dispositions of the subsequent NPNA and, hence, different stoichiometries and modes of antibody binding to rsCSP. Diverse protective antibodies against NANP repeats are therefore not limited to a single germline gene response or mode of binding.

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mAb397 from an RTS,S trial binds NANP repeats of malaria circumsporozoite protein.

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Protective mAb397 is encoded by the VH3-15 gene that is rare for NANP antibodies.

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Anti-NANP mAbs bind type I β-turns in three modes using germline-encoded Trp residues.

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The Trp of mAb397 interacts with Asn instead of Pro in the NPNA type I β-turn.

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Diversity in NANP immune responses can aid in next-generation vaccine design.

Remote Activation of a Latent Epitope in an Autoantigen Decoded With Simulated B-Factors

Mutants of a catalytically inactive variant of Proteinase 3 (PR3)—iPR3-Val¹⁰³ possessing a Ser195Ala mutation relative to wild-type PR3-Val¹⁰³—offer insights into how autoantigen PR3 interacts with antineutrophil cytoplasmic antibodies (ANCAs) in granulomatosis with polyangiitis (GPA) and whether such interactions can be interrupted. Here we report that iHm5-Val¹⁰³, a triple mutant of iPR3-Val¹⁰³, bound a monoclonal antibody (moANCA518) from a GPA patient on an epitope remote from the mutation sites, whereas the corresponding epitope of iPR3-Val¹⁰³ was latent to moANCA518. Simulated B-factor analysis revealed that the binding of moANCA518 to iHm5-Val¹⁰³ was due to increased main-chain flexibility of the latent epitope caused by remote mutations, suggesting rigidification of epitopes with therapeutics to alter pathogenic PR3·ANCA interactions as new GPA treatments.

Potent antibody lineage against malaria transmission elicited by human vaccination with Pfs25

Transmission-blocking vaccines have the potential to be key contributors to malaria elimination. Such vaccines elicit antibodies that inhibit parasites during their development in Anopheles mosquitoes, thus breaking the cycle of transmission. To date, characterization of humoral responses to Plasmodium falciparum transmission-blocking vaccine candidate Pfs25 has largely been conducted in pre-clinical models. Here, we present molecular analyses of human antibody responses generated in a clinical trial evaluating Pfs25 vaccination. From a collection of monoclonal antibodies with transmission-blocking activity, we identify the most potent transmission-blocking antibody yet described against Pfs25; 2544. The interactions of 2544 and three other antibodies with Pfs25 are analyzed by crystallography to understand structural requirements for elicitation of human transmission-blocking responses. Our analyses provide insights into Pfs25 immunogenicity and epitope potency, and detail an affinity maturation pathway for a potent transmission-blocking antibody in humans. Our findings can be employed to guide the design of improved malaria transmission-blocking vaccines.

Pfs25 is a transmission-blocking vaccine candidate for Plasmodium. Here, McLeod et al. analyze the antibody response to Pfs25 in sera from a clinical trial evaluating a Pfs25 vaccine candidate, identify a potent transmission-blocking antibody and determine recognized epitopes on Pfs25.

Abstract 615: Increased somatic hypermutation in the immunoglobulin sequences of melanoma patients who have durable response to checkpoint inhibitor therapy

Patient immune response to tumor can drive profound and durable clinical benefit, but the contribution of antibodies to this benefit is poorly understood. To further our understanding of the role of the humoral response, we compared antibody sequence repertoires of durable responder and non-responder melanoma patients before and during checkpoint inhibitor treatment.

We collected pre- and on-treatment peripheral blood from 26 melanoma patients treated with pembrolizumab (9), ipilimumab (8) or nivolumab+ipilimumab (9). Of the 26 patients, 14 were durable responders (RECIST stable disease, partial response, or complete response for at least 6 months) and 12 were non-responders. We generated natively paired heavy and light chain antibody sequences from individual IgG plasmablasts (CD19+CD20-CD38+CD3-CD14-IgA-IgM-IgD-). Sequences were obtained from a total of 26,725 plasmablasts. These sequences were used to reconstruct lineages (sets of plasmablasts likely derived from a common progenitor B cell) where each lineage shares heavy and light V genes, CDR3 length and 80% sequence similarity in CDR3s.

Durable responders exhibited an increase in somatic hypermutation (SHM) after initiation of treatment. In contrast, no significant change in SHM was observed in non-responders. Higher SHM was also observed in on-treatment repertoires of responders compared with those of non-responders suggesting that T cell checkpoint inhibitors promote activation of humoral immunity in clinical responders. Furthermore, persistent antibody lineages (observed both before and during treatment) showed higher SHM than lineages observed at only a single time point.

Comparison of lineages between patients identified antibodies with high sequence similarity suggesting these antibodies may have arisen from convergent selection, i.e., different patients raising antibodies against shared or similar epitopes. These putative convergent antibodies were enriched in IgG2. IgG2 usage was also higher overall in durable responders than non-responders, even in samples taken prior to treatment. The higher levels of IgG2 observed in responders and in the potentially convergent sets of antibodies suggest that IgG2 antibodies may play a role in effective anti-tumor responses.

In conclusion, our analysis of plasmablast repertoires from melanoma patients suggests that treatment with checkpoint inhibitors promotes SHM in durable responders, and that responder plasmablasts are enriched in IgG2. Moreover, patients make potentially convergent antibodies that are also enriched for the IgG2 subclass. Our observations demonstrate that the humoral immune response is remodeled in patients with anti-tumor responses and support a role for the humoral arm of the immune response in driving clinical benefit in patients treated with checkpoint inhibitors.

Citation Format: Ngan Nguyen, Alusha Mamchak, Mariano Severgnini, Kevin S. Williamson, Xinqi Wu, Elliott F. Drabek, Michael Manos, Xiaomu Chen, Xiaobin Tang, Zoe Amiri, Chantia Carroll, Yvonne Leung, Dongkyoon Kim, Wayne Volkmuth, Norman Greenberg, Daniel Emerling, William H. Robinson, Guy Cavet, F. Stephen Hodi. Increased somatic hypermutation in the immunoglobulin sequences of melanoma patients who have durable response to checkpoint inhibitor therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 615.

Fractional Third and Fourth Dose of RTS,S/AS01 Malaria Candidate Vaccine: A Phase 2a Controlled Human Malaria Parasite Infection and Immunogenicity Study

BACKGROUND

Three full doses of RTS,S/AS01 malaria vaccine provides partial protection against controlled human malaria parasite infection (CHMI) and natural exposure. Immunization regimens, including a delayed fractional third dose, were assessed for potential increased protection against malaria and immunologic responses.

METHODS

In a phase 2a, controlled, open-label, study of healthy malaria-naive adults, 16 subjects vaccinated with a 0-, 1-, and 2-month full-dose regimen (012M) and 30 subjects who received a 0-, 1-, and 7-month regimen, including a fractional third dose (Fx017M), underwent CHMI 3 weeks after the last dose. Plasmablast heavy and light chain immunoglobulin messenger RNA sequencing and antibody avidity were evaluated. Protection against repeat CHMI was evaluated after 8 months.

RESULTS

A total of 26 of 30 subjects in the Fx017M group (vaccine efficacy [VE], 86.7% [95% confidence interval [CI], 66.8%-94.6%]; P < .0001) and 10 of 16 in the 012M group (VE, 62.5% [95% CI, 29.4%-80.1%]; P = .0009) were protected against infection, and protection differed between schedules (P = .040, by the log rank test). The fractional dose boosting increased antibody somatic hypermutation and avidity and sustained high protection upon rechallenge.

DISCUSSIONS

A delayed third fractional vaccine dose improved immunogenicity and protection against infection. Optimization of the RTS,S/AS01 immunization regimen may lead to improved approaches against malaria.

CLINICAL TRIALS REGISTRATION

NCT01857869.

Impact of a multi-biomarker disease activity test on rheumatoid arthritis treatment decisions and therapy use

OBJECTIVE

To assess how use of a multi-biomarker disease activity (MBDA) blood test for rheumatoid arthritis (RA) affects treatment decisions made by health care providers (HCPs) in clinical practice.

RESEARCH DESIGN AND METHODS

At routine office visits, 101 patients with RA were assessed by their HCPs (N = 6), and they provided blood samples for MBDA testing. HCPs completed surveys before and after viewing the MBDA test result, recording dosage and frequency for all planned RA medications and physician global assessment of disease activity. Frequency and types of change in treatment plan that resulted from viewing the MBDA test result were determined.

MAIN OUTCOME MEASURE

Percentage of cases in which the HCP changed the planned treatment after viewing the MBDA test result.

RESULTS

Prior to HCP review of the MBDA test, disease modifying anti-rheumatic drug (DMARD) use by the 101 patients included methotrexate in 62% of patients; hydroxychloroquine 29%; TNF inhibitor 42%; non-TNF inhibitor biologic agent 19%; and other drugs at lower frequencies. Review of MBDA test results changed HCP treatment decisions in 38 cases (38%), of which 18 involved starting, discontinuing or switching a biologic or non-biologic DMARD. Other changes involved drug dosage, frequency or route of administration. The total frequency of use of the major classes of drug therapy changed by <5%. Treatment plans changed 63% of the time when the MBDA test result was perceived as being not consistent or somewhat consistent with the HCP assessment of disease activity.

STUDY LIMITATIONS

Limited sample size; lack of control group; no longitudinal follow-up.

CONCLUSIONS

The addition of the MBDA test to clinical assessment led to meaningful changes in the treatment plans of 38% of RA patients being cared for by HCPs in office practice. Even though treatment was potentially improved, the overall quantity of drug use was minimally affected.

TRPM8 biology and medicinal chemistry

TRPM8 belongs to the TRPM Melastatin subfamily of Transient Receptor Potential (TRP) ion channels. Activated by cool temperatures and mimetic ligands, such as menthol and icilin, TRPM8 has been shown to play a role in thermoreception and is expressed in peripheral nerves. TRPM8 is also expressed in other tissues which are not exposed to temperature fluctuations, such as the prostate. The recent advancement of a TRPM8 agonist into the clinic for the treatment of prostate cancer suggests that the channel plays a role in some human pathologies. As more drug-like and selective agonists and antagonists of TRPM8 become available, in vivo pharmacology studies will complement already published knockout data to further our understanding of the role of TRPM8 in human disease.

Prostaglandin F2 alpha enhances tyrosine phosphorylation and DNA synthesis through phospholipase C-coupled receptor via Ca(2+)-dependent intracellular pathway in NIH-3T3 cells

Previously, we characterized the prostaglandin (PG) F2 alpha receptor linked to phospholipase C activation and DNA synthesis in NIH-3T3 cells (Nakao, A., Watanabe, T., Taniguchi, S., Nakamura, M., Honda, Z-I., Shimizu, T., and Kurokawa, K. (1993) J. Cell. Physiol. 155, 257-264). To elucidate intracellular events evoked via this receptor, we examined changes caused by PGF2 alpha stimulation in the phosphotyrosine composition of cellular proteins. The addition of PGF2 alpha to cells in quiescent culture rapidly increased the levels of phosphotyrosine in cellular proteins with Mr values of 70,000 (pp70), 85,000 (pp85), 92,000 (pp92), 100,000 (pp100), and 125,000 (pp125); the latter was immunologically identified as p125 focal adhesion kinase. The PGF2 alpha-induced changes in the level of intracellular Ca2+ ([Ca2+]i) elevation, formation of inositol phosphates, and [3H]thymidine incorporation followed a similar dose dependence as PGF2 alpha-induced tyrosine phosphorylation. This tyrosine phosphorylation was independent of extracellular Ca2+, while a [Ca2+]i chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (50 microM), completely inhibited the PGF2 alpha-induced elevation of [Ca2+]i, tyrosine phosphorylation, and [3H]thymidine incorporation. Ionomycin (0.1 microM), which induced [Ca2+]i elevation without formation of inositol phosphates, mimicked the PGF2 alpha-induced tyrosine phosphorylation. 12-O-Tetradecanoylphorbol-13-acetate (TPA) also induced [3H]thymidine incorporation in a dose-dependent manner but had no significant effect on tyrosine phosphorylation. The PGF2 alpha-induced tyrosine phosphorylation could be observed even in the cells pretreated with TPA (5 microM, 24 h). PGF2 alpha exhibited an additive effect on TPA-induced [3H]thymidine incorporation but had no effect on the 32P-phosphorylation of a known 80-kDa protein kinase (PK) C substrate. Both staurosporine and H-7 inhibited the PGF2 alpha-induced increase in [3H]thymidine incorporation and tyrosine phosphorylation in a similar dose-dependent manner whether or not cells were pretreated with TPA (5 microM, 24 h). However, W-7 and KN-62 had no effect on these cellular responses even at the concentration for the almost complete inhibition of Ca2+/calmodulin-dependent PKs (20 microM). These results, taken together, indicate that PGF2 alpha receptor-mediated tyrosine phosphorylation is evoked by a [Ca2+]i-dependent mechanism that is sensitive to staurosporine and H-7 but which is independent of PKC or Ca2+/calmodulin PKs. Finally, the data suggest that this PGF2 alpha-induced signaling pathway is linked to the proliferation of cells.