Treatment Patterns and Real-World Outcomes for Locally Advanced or Metastatic Urothelial Cancer in the Era of Immunotherapy.

BACKGROUND AND OBJECTIVE: There are limited data on real-world outcomes for patients with advanced or metastatic urothelial cancer (mUC) since immune checkpoint inhibitors (ICIs) became available. Our objective was to analyze outcomes for patients with mUC since ICIs became available. METHODS: We performed a retrospective analysis of 131 patients with mUC attending the outpatient clinic of a single tertiary care center who received systemic therapy between June 2017 and July 2021 with follow-up up to December 2022. Summary and descriptive statistics were calculated for categorical and continuous variables. The Kaplan-Meier method was applied to calculate survival, and a Cox proportional-hazards model was used to explore associations between clinical variables and outcomes. KEY FINDINGS AND LIMITATIONS: The median patient age was 68 yr (range 35-90). The first systemic therapy administered was platinum-based in 79% of cases and ICI-based in 21%. Some 61% of the cohort received a second systemic treatment, with 75% of these an ICI. Median overall survival for the entire cohort was 24 mo (interquartile range 9-35). Patients on ICI therapy for ≥6 mo had median overall survival of 59 mo (95% confidence interval 39 mo-not reached). Metastatic sites on initiation of ICI therapy and C-reactive protein kinetics were prognostic in patients receiving ICIs. Limitations include the retrospective design and inherent selection bias. CONCLUSIONS AND CLINICAL IMPLICATIONS: More than 60% of patients with mUC received second-line treatment, and 75% of these received an ICI. Patients staying on immunotherapy for more than 6 mo have substantially better outcomes in comparison to patients with less time on immunotherapy and historical cohorts. PATIENT SUMMARY: We looked at the lines of therapy and outcomes for patients with advanced or metastatic cancer of the urinary tract, starting from when immunotherapy drugs called immune checkpoint inhibitors (ICIs) became available. We found that 60% of patients have received second-line therapy, which is a double the rate in comparison to historical groups of patients. Patients with long-term ICI therapy (>6 months) had significantly better outcomes, with a median survival of more than 3 years.

Performance of clinical risk scores and prediction models to identify pathogenic germline variants in patients with advanced prostate cancer.

PURPOSE: Determining the frequency and distribution of pathogenic germline variants (PGVs) in Austrian prostate cancer (PCa) patients and to assess the accuracy of different clinical risk scores to correctly predict PGVs. METHODS: This cross-sectional study included 313 men with advanced PCa. A comprehensive personal and family history was obtained based on predefined questionnaires. Germline DNA sequencing was performed between 2019 and 2021 irrespective of family history, metastatic or castration status or age at diagnosis. Clinical risk scores for hereditary cancer syndromes were evaluated and a PCa-specific score was developed to assess the presence of PGVs. RESULTS: PGV presence was associated with metastasis (p = 0.047) and castration resistance (p = 0.011), but not with personal cancer history or with relatives with any type of cancer. Clinical risk scores (Manchester score, PREMM5 score, Amsterdam II criteria or Johns Hopkins criteria) showed low sensitivities (3.3-20%) for assessing the probability of PGV presence. A score specifically designed for PCa patients stratifying patients into low- or high-risk regarding PGV probability, correctly classified all PGV carriers as high-risk, whereas a third of PCa patients without PGVs was classified as low risk of the presence of PGVs. CONCLUSION: Application of common clinical risk scores based on family history are not suitable to identify PCa patients with high PGV probabilities. A PCa-specific score stratified PCa patients into low- or high-risk of PGV presence with sufficient accuracy, and germline DNA sequencing may be omitted in patients with a low score. Further studies are needed to evaluate the score.

Blood-Based Biomarkers as Prognostic Factors of Recurrent Disease after Radical Cystectomy: A Systematic Review and Meta-Analysis.

Survival outcomes after radical cystectomy (RC) for bladder cancer (BCa) have not improved in recent decades; nevertheless, RC remains the standard treatment for patients with localized muscle-invasive BCa. Identification of the patients most likely to benefit from RC only versus a combination with systemic therapy versus systemic therapy first/only and bladder-sparing is needed. This systematic review and meta-analysis pools the data from published studies on blood-based biomarkers to help prognosticate disease recurrence after RC. A literature search on PubMed and Scopus was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. Articles published before November 2022 were screened for eligibility. A meta-analysis was performed on studies investigating the association of the neutrophil-to-lymphocyte ratio (NLR), the only biomarker with sufficient data, with recurrence-free survival. The systematic review identified 33 studies, and 7 articles were included in the meta-analysis. Our results demonstrated a statistically significant correlation between elevated NLR and an increased risk of disease recurrence (HR 1.26; 95% CI 1.09, 1.45; p = 0.002) after RC. The systematic review identified various other inflammatory biomarkers, such as interleukin-6 or the albumin-to-globulin ratio, which have been reported to have a prognostic impact on recurrence after RC. Besides that, the nutritional status, factors of angiogenesis and circulating tumor cells, and DNA seem to be promising tools for the prognostication of recurrence after RC. Due to the high heterogeneity between the studies and the different cut-off values of biomarkers, prospective and validation trials with larger sample sizes and standardized cut-off values should be conducted to strengthen the approach in using biomarkers as a tool for risk stratification in clinical decision-making for patients with localized muscle-invasive BCa.

Quantitative Acetylomics Uncover Acetylation-Mediated Pathway Changes Following Histone Deacetylase Inhibition in Anaplastic Large Cell Lymphoma.

Histone deacetylases (HDACs) target acetylated lysine residues in histone and non-histone proteins. HDACs are implicated in the regulation of genomic stability, cell cycle, cell death and differentiation and thus critically involved in tumorigenesis. Further, HDACs regulate T-cell development and HDAC inhibitors (HDACis) have been approved for clinical use in some T-cell malignancies. Still, the exact targets and mechanisms of HDAC inhibition in cancer are understudied. We isolated tumor cell lines from a transgenic mouse model of anaplastic large cell lymphoma (ALCL), a rare T-cell lymphoma, and abrogated HDAC activity by treatment with the HDACis Vorinostat and Entinostat or Cre-mediated deletion of Hdac1. Changes in overall protein expression as well as histone and protein acetylation were measured following Hdac1 deletion or pharmacological inhibition using label-free liquid chromatography mass spectrometry (LC-MS/MS). We found changes in overall protein abundance and increased acetylation of histones and non-histone proteins, many of which were newly discovered and associated with major metabolic and DNA damage pathways. For non-histone acetylation, we mapped a total of 1204 acetylated peptides corresponding to 603 proteins, including chromatin modifying proteins and transcription factors. Hyperacetylated proteins were involved in processes such as transcription, RNA metabolism and DNA damage repair (DDR). The DDR pathway was majorly affected by hyperacetylation following HDAC inhibition. This included acetylation of H2AX, PARP1 and previously unrecognized acetylation sites in TP53BP1. Our data provide a comprehensive view of the targets of HDAC inhibition in malignant T cells with general applicability and could have translational impact for the treatment of ALCL with HDACis alone or in combination therapies.

Molecular uropathology and cancer genetics for the urologist: key findings for classification and diagnosis.

PURPOSE OF REVIEW: To highlight the latest changes in prostate cancer (PCa), urothelial carcinoma, upper tract urothelial carcinoma (UTUC) and renal cell carcinoma (RCC) diagnosis and the impact of genetics in this field. RECENT FINDINGS: Breast cancer1/2 mutations start to play a major role in PCa treatment with regard to personalized medicine. In urothelial carcinoma an overlap between histological pathological and molecular findings exists, fibroblast growth factor receptor alteration are starting to play a major role, programmed death-ligand 1 although problematic is still important in the treatment setting. UTUC is rare, but genetically different from urothelial carcinoma. In the development of RCC, different genetic pathways such as Von Hippel-Lindau, but also tuberous sclerosis 1/2 and others play a major role in tumor development. SUMMARY: Over the last years, genetics has become increasingly important role in the diagnosis and the treatment of patients with urological malignancies. The upcoming 5th edition (1) of the WHO still considers conventional surgical pathology as the diagnostic gold standard, but molecular pathology is gaining importance not only for diagnosis, but also in personalized treatment, of prostate, kidney cancer and urothelial carcinomas. Therefore, a close collaboration between surgical urology, pathology and oncology departments is mandatory. In this review, we will discuss the latest evolutions in PCa, urothelial carcinoma, upper urinary tract carcinomas and RCC s in the field of genetics in urology.

Evaluation of APOBEC3 expression as prognostic marker in squamous cell carcinoma of the penis.

Squamous cell carcinoma of the penis (PSC) is a rare disease with limited information on the molecular events leading to malignant transformation. In a third of PSC cases, presence of human papilloma virus (HPV) is found. The APOBEC3 family of proteins is known to play a significant role in defense against HPV infection, but their role in PSC is largely unknown. In this study, we aim to assess mRNA expression levels of APOBEC3 family members in HPV+ and HPV- PSC to get insight into their association with clinicopathological features and to evaluate their prognostic impact. Expression levels of six APOBEC3 family members in tissue from 50 patients with PSC were determined by RT-PCR and correlated with clinical and histopathological features. Lower expression of APOBEC3A, APOBEC3B, and APOBEC3C was observed in advanced PSC stages. Except for APOBEC3D, HPV+ samples showed higher expression of APOBEC3s compared to HPV- samples. In univariate analyses, APOBEC3A and APOBEC3C expression tended to be associated with disease-free survival and APOBEC3A expression with overall survival; however, multivariable analyses failed to confirm these associations with outcome. More extensive external validation and functional laboratory studies are needed to evaluate further their role in PSC development and progression.

Basal cell carcinoma of the prostate: a case report responding to the FGFR inhibitor pemigatinib and literature review.

PURPOSE OF REVIEW: Due to the limited number of cases, there are no guidelines for basal cell carcinoma (BCC) of the prostate. This review combines an unpublished case report of a 55-year-old patient with BCC with an assessment of the latest literature. RECENT FINDINGS: BCC of the prostate has previously been described in only approximately 140 cases. We describe the diagnostic process, including the uropathological and DNA-sequencing results, which allowed us to start an experimental treatment with pemigatinib. BCC of the prostate is associated with an aggressive biological and clinical behavior, such as recurrence and metastasis. Several immunohistochemical stainings are available to differentiate BCC from adenocarcinoma of the prostate. Based on pathology and results from next-generation sequencing (NGS), patients can be offered targeted therapies. SUMMARY: With the aid of histological work-up and immunostaining, prostatic BCC can be accurately diagnosed. Our patient underwent radical prostatectomy and staged extended lymphadenectomy due to lymph node recurrence. The patient subsequently developed progressive disease and was treated with the FGFR-inhibitor pemigatinib. The patient's liver metastasis significantly responded. The present case confirms the possibility of aggressive behavior of prostatic BCC and highlights the importance of a thorough uropathological and molecular biological analysis with a precision medicine strategy.

Circulating Tumour DNA Is a Strong Predictor of Outcomes in Patients Treated with Systemic Therapy for Urothelial Carcinoma.

We summarise the available data for and assess the prognostic value of circulating tumour DNA (ctDNA) in patients treated with systemic therapy for urothelial carcinoma (UC). Studies were deemed eligible if they reported on oncologic outcomes for patients with UC treated with systemic therapy according to the baseline ctDNA profile (before starting systemic therapy) and/or changes over the course of therapy. Five studies met the eligibility criteria. We found a strong association between high baseline ctDNA levels and worse disease-free survival (DFS; hazard ratio [HR] 3.53, 95% confidence interval [CI] 2.58-4.84) and overall survival (OS; HR 2.99, 95% CI 2.17-4.13). Patients with a decline in ctDNA level after immunotherapy had better DFS (HR 0.25, 95% CI 0.13-0.49) and OS (HR 0.10, 95% CI 0.03-0.42) in comparison to patients without a ctDNA decline. Conversely, an increase in ctDNA levels after immunotherapy was associated with worse survival outcomes. Patients with UC who exhibited a decrease in ctDNA levels during systemic therapy had better survival outcomes compared to those with stable or increasing ctDNA levels. PATIENT SUMMARY: Measurement of tumour DNA in blood may help in identifying patients with cancer of the urinary tract who are unlikely to respond to chemotherapy or immunotherapy. This could serve as a biomarker for monitoring cancer treatment.

Molecular and Pharmacological Bladder Cancer Therapy Screening: Discovery of Clofarabine as a Highly Active Compound.

BACKGROUND: The heterogeneity of bladder cancers (BCs) is a major challenge for the development of novel therapies. However, given the high rates of recurrence and/or treatment failure, the identification of effective therapeutic strategies is an urgent clinical need. OBJECTIVE: We aimed to establish a model system for drug identification/repurposing in order to identify novel therapies for the treatment of BC. DESIGN, SETTING, AND PARTICIPANTS: A collection of commercially available BC cell lines (n = 32) was comprehensively characterized. A panel of 23 cell lines, representing a broad spectrum of BC, was selected to perform a high-throughput drug screen. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Positive hits were defined as compounds giving >50% inhibition in at least one BC cell line. RESULTS AND LIMITATIONS: Amongst >1700 tested chemical compounds, a total of 471 substances exhibited antineoplastic effects. Clofarabine, an antimetabolite drug used as third-line treatment for childhood acute lymphoblastic leukaemia, was amongst the limited number of drugs with inhibitory effects on cell lines of all intrinsic subtypes. We, thus, reassessed the substance and confirmed its inhibitory effects on commercially available cell lines and patient-derived cell cultures representing various disease stages, intrinsic subtypes, and histologic variants. To verify these effects in vivo, a patient-derived cell xenograft model for urothelial carcinoma (UC) was used. Well-tolerated doses of clofarabine induced complete remission in all treated animals (n = 12) suffering from both early- and late-stage disease. We further took advantage of another patient-derived cell xenograft model originating from the rare disease entity sarcomatoid carcinoma (SaC). Similarly to UC xenograft mice, clofarabine induced subcomplete to complete tumour remissions in all treated animals (n = 8). CONCLUSIONS: The potent effects of clofarabine in vitro and in vivo suggest that our findings may be of high clinical relevance. Clinical trials are needed to assess the value of clofarabine in improving BC patient care. PATIENT SUMMARY: We used commercially available cell lines for the identification of novel drugs for the treatment of bladder cancer. We confirmed the effects of one of these drugs, clofarabine, in patient-derived cell lines and two different mouse models, thereby demonstrating a potential clinical relevance of this substance in bladder cancer treatment.

Molecular intricacies of upper tract urothelial carcinoma and their relevance for therapy considerations.

PURPOSE OF REVIEW: The aim of this study was to give an overview of molecular alterations in upper tract urothelial carcinomas (UTUCs) and to discuss them in the context of current and prospective systemic therapies. RECENT FINDINGS: UTUCs not only share a similar molecular landscape with urothelial carcinoma of the bladder (UCB), but also have distinct molecular features that can have an impact on therapy selection. FGFR3 alterations occur with a significant higher frequency in UTUC, with up to 40% of tumours harbouring FGFR3 driver mutations compared with 20% in UCB. In addition, a substantial number of high-grade UTUC show an immune-depleted phenotype and a luminal papillary expression subtype, thus predisposing them for FGFR inhibitor treatment. Approximately 20% of UTUC tumours have acquired mutations in TP53 and demonstrate a significant degree of genomic instability, which makes them candidates for systemic chemotherapy or immunotherapy. Whereas microsatellite instability (MSI) is rare in sporadic UTUC, 5-10% of UTUC patients have germline mutations in DNA mismatch repair genes, which leads to high MSI with enriched neoantigen load and presumably better response rates to immunotherapy. SUMMARY: Treatment decisions in UTUC should take molecular tumour characteristics into account. The currently most therapy-relevant molecular alterations in UTUC comprise FGFR3 mutational status and mutations in DNA mismatch repair genes with concomitant microsatellite instability.

Expression Analysis and Mutational Status of Histone Methyltransferase KMT2D at Different Upper Tract Urothelial Carcinoma Locations.

The gene coding for histone methyltransferase KMT2D is found among the top mutated genes in upper tract urothelial carcinoma (UTUC); however, there is a lack of data regarding its association with clinicopathologic features as well as survival outcomes. Therefore, we aimed to investigate KMT2D expression, mutation patterns, and their utility as prognostic biomarkers in patients with UTUC. A single-center study was conducted on tumor specimens from 51 patients treated with radical nephroureterectomy (RNU). Analysis of KMT2D protein expression was performed using immunohistochemistry (IHC). Customized next-generation sequencing (NGS) was used to assess alterations in KMT2D exons. Cox regression was used to assess the relationship of KMT2D protein expression and mutational status with survival outcomes. KMT2D expression was increased in patients with a previous history of bladder cancer (25% vs. 0%, p = 0.02). The NGS analysis of KMT2D exons in 27 UTUC tumors revealed a significant association between pathogenic KMT2D variants and tumor location (p = 0.02). Pathogenic KMT2D variants were predominantly found in patients with non-pelvic or multifocal tumors (60% vs. 14%), while the majority of patients with a pelvic tumor location (81% vs. 20%) did not harbor pathogenic KMT2D alterations. Both IHC and NGS analyses of KMT2D failed to detect a statistically significant association between KMT2D protein or KMT2D gene alteration status and clinical variables such as stage/grade of the disease or survival outcomes (all p > 0.05). KMT2D alterations and protein expression were associated with UTUC features such as multifocality, ureteral location, and previous bladder cancer. While KMT2D protein expression and KMT2D mutational status do not seem to have prognostic value in UTUC, they appear to add information to improve clinical decision-making regarding the type of therapy.

Single-lesion Prostate-specific Membrane Antigen Protein Expression (PSMA) and Response to [177Lu]-PSMA-ligand Therapy in Patients with Castration-resistant Prostate Cancer.

Initial reports of a clinical response in patients treated with the radioligand [177Lu]-PSMA-617 for castration-resistant prostate cancer (CRPC) are promising, despite known inter- and intrapatient heterogeneity. In metastatic CRPC, we examined the association of baseline immunohistochemical (IHC) expression of prostate-specific membrane antigen (PSMA) in a single lesion and responsiveness to [177Lu]-PSMA-617 therapy, measured as the PSMA maximum standardized uptake value (SUVmax). Between 2015 and 2020, 19 patients with multiple metastases underwent single-lesion biopsy, [68Ga]-PSMA positron emission tomography (PET) imaging, and treatment with [177Lu]-PSMA-617. A monoclonal anti-PSMA antibody was used to semiquantitatively assess PSMA IHC in the biopsy specimen. Imaging evaluation of the biopsied single lesion and overall response was performed according to Positron Emission Tomography Response Criteria in Solid Tumors. The PSMA IHC histoscore correlated positively with pretreatment same-site PSMA SUVmax (r s = 0.6). Nine patients had imaging after three cycles of [177Lu]-PSMA-617 and were included in the lesion-specific analysis. Of these, five patients (55.6%) had an SUVmax response at the biopsy site, but three experienced overall progression. The histoscore was unable to predict the lesion-specific change in SUVmax (95% confidence interval [CI] -44.2 to 69.2) or PSA (95% CI-125.2 to 17.2). There was no correlation between single-lesion SUVmax and overall progression (r s = 0.1) on [68Ga]-PSMA PET imaging. Additional studies need to interrogate the clinical consequence of PSMA expression heterogeneity in metastases and the association with response to [177Lu]-PSMA-671. PATIENT SUMMARY: Treatment with a radioactive binding molecule called [177Lu]-PSMA-617 for men with prostate cancer resistant to castration (CRPC) is showing promise. We investigated the association between the presence of PSMA protein in metastatic lesions at biopsy and response to [177Lu]-PSMA-617 among men with metastatic CRPC. We found that assessment of PSMA presence at biopsy is not a reliable predictor of response to [177Lu]-PSMA-617. Additional studies are needed to better determine which CRPC metastatic sites will respond to this therapy.

Requirement of DNMT1 to orchestrate epigenomic reprogramming for NPM-ALK-driven lymphomagenesis.

Malignant transformation depends on genetic and epigenetic events that result in a burst of deregulated gene expression and chromatin changes. To dissect the sequence of events in this process, we used a T-cell-specific lymphoma model based on the human oncogenic nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) translocation. We find that transformation of T cells shifts thymic cell populations to an undifferentiated immunophenotype, which occurs only after a period of latency, accompanied by induction of the MYC-NOTCH1 axis and deregulation of key epigenetic enzymes. We discover aberrant DNA methylation patterns, overlapping with regulatory regions, plus a high degree of epigenetic heterogeneity between individual tumors. In addition, ALK-positive tumors show a loss of associated methylation patterns of neighboring CpG sites. Notably, deletion of the maintenance DNA methyltransferase DNMT1 completely abrogates lymphomagenesis in this model, despite oncogenic signaling through NPM-ALK, suggesting that faithful maintenance of tumor-specific methylation through DNMT1 is essential for sustained proliferation and tumorigenesis.

Thyroid and androgen receptor signaling are antagonized by µ-Crystallin in prostate cancer.

Androgen deprivation therapy (ADT) remains a key approach in the treatment of prostate cancer (PCa). However, PCa inevitably relapses and becomes ADT resistant. Besides androgens, there is evidence that thyroid hormone thyroxine (T4) and its active form 3,5,3'-triiodo-L-thyronine (T3) are involved in the progression of PCa. Epidemiologic evidences show a higher incidence of PCa in men with elevated thyroid hormone levels. The thyroid hormone binding protein µ-Crystallin (CRYM) mediates intracellular thyroid hormone action by sequestering T3 and blocks its binding to cognate receptors (TRα/TRß) in target tissues. We show in our study that low CRYM expression levels in PCa patients are associated with early biochemical recurrence and poor prognosis. Moreover, we found a disease stage-specific expression of CRYM in PCa. CRYM counteracted thyroid and androgen signaling and blocked intracellular choline uptake. CRYM inversely correlated with [18F]fluoromethylcholine (FMC) levels in positron emission tomography/magnetic resonance imaging of PCa patients. Our data suggest CRYM as a novel antagonist of T3- and androgen-mediated signaling in PCa. The role of CRYM could therefore be an essential control mechanism for the prevention of aggressive PCa growth.

Discovery of Molecular DNA Methylation-Based Biomarkers through Genome-Wide Analysis of Response Patterns to BCG for Bladder Cancer.

BACKGROUND: Bacillus Calmette-Guérin (BCG) immunotherapy, the standard adjuvant intravesical therapy for some intermediate and most high-risk non-muscle invasive bladder cancers (NMIBCs), suffers from a heterogenous response rate. Molecular markers to help guide responses are scarce and currently not used in the clinical setting. METHODS: To identify novel biomarkers and pathways involved in response to BCG immunotherapy, we performed a genome-wide DNA methylation analysis of NMIBCs before BCG therapy. Genome-wide DNA methylation profiles of DNA isolated from tumors of 26 BCG responders and 27 failures were obtained using the Infinium MethylationEPIC BeadChip. RESULTS: Distinct DNA methylation patterns were found by genome-wide analysis in the two groups. Differentially methylated CpG sites were predominantly located in gene promoters and gene bodies associated with bacterial invasion of epithelial cells, chemokine signaling, endocytosis, and focal adhesion. In total, 40 genomic regions with a significant difference in methylation between responders and failures were detected. The differential methylation state of six of these regions, localized in the promoters of the genes GPR158, KLF8, C12orf42, WDR44, FLT1, and CHST11, were internally validated by bisulfite-sequencing. GPR158 promoter hypermethylation was the best predictor of BCG failure with an AUC of 0.809 (p-value < 0.001). CONCLUSIONS: Tumors from BCG responders and BCG failures harbor distinct DNA methylation profiles. Differentially methylated DNA regions were detected in genes related to pathways involved in bacterial invasion of cells or focal adhesion. We identified candidate DNA methylation biomarkers that may help to predict patient prognosis after external validation in larger, well-designed cohorts.

Channelrhodopsin-mediated optogenetics highlights a central role of depolarization-dependent plant proton pumps.

In plants, environmental stressors trigger plasma membrane depolarizations. Being electrically interconnected via plasmodesmata, proper functional dissection of electrical signaling by electrophysiology is basically impossible. The green alga Chlamydomonas reinhardtii evolved blue light-excited channelrhodopsins (ChR1, 2) to navigate. When expressed in excitable nerve and muscle cells, ChRs can be used to control the membrane potential via illumination. In Arabidopsis plants, we used the algal ChR2-light switches as tools to stimulate plasmodesmata-interconnected photosynthetic cell networks by blue light and monitor the subsequent plasma membrane electrical responses. Blue-dependent stimulations of ChR2 expressing mesophyll cells, resting around -160 to -180 mV, reproducibly depolarized the membrane potential by 95 mV on average. Following excitation, mesophyll cells recovered their prestimulus potential not without transiently passing a hyperpolarization state. By combining optogenetics with voltage-sensing microelectrodes, we demonstrate that plant plasma membrane AHA-type H+-ATPase governs the gross repolarization process. AHA2 protein biochemistry and functional expression analysis in Xenopus oocytes indicates that the capacity of this H+ pump to recharge the membrane potential is rooted in its voltage- and pH-dependent functional anatomy. Thus, ChR2 optogenetics appears well suited to noninvasively expose plant cells to signal specific depolarization signatures. From the responses we learn about the molecular processes, plants employ to channel stress-associated membrane excitations into physiological responses.