Trophoblast cell surface antigen 2 (Trop-2) phosphorylation by protein kinase C α/δ (PKCα/δ) enhances cell motility

Trop2-targeted therapy in breast cancer

Human trophoblastic cell surface antigen 2 (Trop2) is a glycoprotein, a cellular marker of trophoblastic and stem cells, and a calcium signaling transducer involved in several signaling pathways, leading to the proliferation, invasion, and metastasis of tumors. It is expressed at a low level in normal epithelial cells, but at a high level in many tumors, making it an ideal target for cancer therapy. According to previous literature, Trop2 is broadly expressed in all breast cancer subtypes, especially in triple negative breast cancer (TNBC). Several clinical trials have demonstrated the effectiveness of Trop2-targeted therapy in breast cancer. Sacituzumab govitecan (SG) is a Trop2-targeted antibody-drug conjugate (ADC) that has been approved for the treatment of metastatic TNBC and hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer. This article reviews the structure and function of Trop2, several major Trop2-targeted ADCs, other appealing novel Trop2-targeted agents and relevant clinical trials to provide a landscape of how Trop2-targeted treatments will develop in the future.

Phylogenetic conservation of Trop-2 across species-rodent and primate genomics model anti-Trop-2 therapy for pre-clinical benchmarks

A phylogenetic conservation analysis of Trop-2 across vertebrate species showed a high degree of sequence conservation, permitting to explore multiple models as pre-clinical benchmarks. Sequence divergence and incomplete conservation of expression patterns were observed in mouse and rat. Primate Trop-2 sequences were found to be 95%-100% identical to the human sequence. Comparative three-dimension primate Trop-2 structures were obtained with AlphaFold and homology modeling. This revealed high structure conservation of Trop-2 (0.66 ProMod3 GMQE, 0.80-0.86 ± 0.05 QMEANDisCo scores), with conservative amino acid changes at variant sites. Primate TACSTD2/TROP2 cDNAs were cloned and transfectants for individual ORF were shown to be efficiently recognized by humanized anti-Trop-2 monoclonal antibodies (Hu2G10, Hu2EF). Immunohistochemistry analysis of Macaca mulatta (rhesus monkey) tissues showed Trop-2 expression patterns that closely followed those in human tissues. This led us to test Trop-2 targeting in vivo in Macaca fascicularis (cynomolgus monkey). Intravenously injected Hu2G10 and Hu2EF were well tolerated from 5 to 10 mg/kg. Neither neurological, respiratory, digestive, urinary symptoms, nor biochemical or hematological toxicities were detected during 28-day observation. Blood serum pharmacokinetic (PK) studies were conducted utilizing anti-idiotypic antibodies in capture-ELISA assays. Hu2G10 (t1/2 = 6.5 days) and Hu2EF (t1/2 = 5.5 days) were stable in plasma, and were detectable in the circulation up to 3 weeks after the infusion. These findings validate primates as reliable models for Hu2G10 and Hu2EF toxicity and PK, and support the use of these antibodies as next-generation anti-Trop-2 immunotherapy tools.

Targeting Trop2 in solid tumors: a look into structures and novel epitopes

Trophoblast cell surface antigen 2 (Trop2) exhibits limited expression in normal tissues but is over-expressed across various solid tumors. The effectiveness of anti-Trop2 antibody-drug conjugate (ADC) in managing breast cancer validates Trop2 as a promising therapeutic target for cancer treatment. However, excessive toxicity and a low response rate of ADCs pose ongoing challenges. Safer and more effective strategies should be developed for Trop2-positive cancers. The dynamic structural attributes and the oligomeric assembly of Trop2 present formidable obstacles to the progression of innovative targeted therapeutics. In this review, we summarize recent advancements in understanding Trop2's structure and provide an overview of the epitope characteristics of Trop2-targeted agents. Furthermore, we discuss the correlation between anti-Trop2 agents' epitopes and their respective functions, particularly emphasizing their efficacy and specificity in targeted therapies.

The Relationship between Trop-2, Chemotherapeutic Drugs, and Chemoresistance

Trop-2 is a highly conserved one-pass transmembrane mammalian glycoprotein that is normally expressed in tissues such as the lung, intestines, and kidney during embryonic development. It is overexpressed in many epithelial cancers but is absent in non-epithelial tumors. Trop-2 is an intracellular calcium signal transducer that participates in the promotion of cell proliferation, migration, invasion, metastasis, and probably stemness. It also has some tumor suppressor effects. The pro-tumoral actions have been thoroughly investigated and reported. However, Trop-2's activity in chemoresistance is less well known. We review a possible relationship between Trop-2, chemotherapy, and chemoresistance. We conclude that there is a clear role for Trop-2 in some specific chemoresistance events. On the other hand, there is no clear evidence for its participation in multidrug resistance through direct drug transport. The development of antibody conjugate drugs (ACD) centered on anti-Trop-2 monoclonal antibodies opened the gates for the treatment of some tumors resistant to classic chemotherapies. Advanced urothelial tumors and breast cancer were among the first malignancies for which these ACDs have been employed. However, there is a wide group of other tumors that may benefit from anti-Trop-2 therapy as soon as clinical trials are completed.

An assembly of TROP2-mediated signaling events

Trophoblast cell surface antigen 2 (TROP2) is a calcium-transducing transmembrane protein mainly involved in embryo development. The aberrant expression of TROP2 is observed in numerous cancers, including triple-negative breast cancer, gastric, colorectal, pancreatic, squamous cell carcinoma of the oral cavity, and prostate cancers. The main signaling pathways mediated by TROP2 are calcium signaling, PI3K/AKT, JAK/STAT, MAPKs, and β-catenin signaling. However, collective information about the TROP2-mediated signaling pathway is not available for visualization or analysis. In this study, we constructed a TROP2 signaling map with respect to its role in different cancers. The data curation was done manually by following the NetPath annotation criteria. The described map consists of different molecular events, including 8 activation/inhibition, 16 enzyme catalysis, 19 gene regulations, 12 molecular associations, 39 induced-protein expressions, and 2 protein translocation. The data of the TROP2 pathway map is made freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5300 ). Development of TROP2 signaling pathway map.

Epigenetically upregulating TROP2 and SLFN11 enhances therapeutic efficacy of TROP2 antibody drug conjugate sacitizumab govitecan

TROP2 antibody drug conjugates (ADCs) are under active development. We seek to determine whether we can enhance activity of TROP2 ADCs by increasing TROP2 expression. In metaplastic breast cancers (MpBC), there is limited expression of TROP2, and downregulating transcription factor ZEB1 upregulates E-cad and TROP2, thus sensitizing cancers to TROP2 ADC sacituzumab govitecan (SG). Demethylating agent decitabine decreases DNA methyltransferase expression and TROP2 promoter methylation and subsequently increases TROP2 expression. Decitabine treatment as well as overexpression of TROP2 significantly enhance SG antitumor activity. Decitabine also increases SLFN11, a biomarker of topoisomerase 1 inhibitor (TOP1) sensitivity and is synergistic with SG which has a TOP1 payload, in TROP2-expressing SLFN11-low BC cells. In conclusion, TROP2 and SLFN11 expression can be epigenetically modulated and the combination of demethylating agent decitabine with TROP2 ADCs may represent a novel therapeutic approach for tumors with low TROP2 or SLFN11 expression.

Trophoblast cell surface antigen-2 phosphorylation triggered by binding of galectin-3 drives metastasis through down-regulation of E-cadherin

The expression of trophoblast cell surface antigen-2 (Trop-2) is enhanced in many tumor tissues and is correlated with increased malignancy and poor survival of patients with cancer. Previously, we demonstrated that the Ser-322 residue of Trop-2 is phosphorylated by protein kinase Cα (PKCα) and PKCδ. Here, we demonstrate that phosphomimetic Trop-2 expressing cells have markedly decreased E-cadherin mRNA and protein levels. Consistently, mRNA and protein of the E-cadherin-repressing transcription factors zinc finger E-Box binding homeobox 1 (ZEB1) were elevated, suggesting transcriptional regulation of E-cadherin expression. The binding of galectin-3 to Trop-2 enhanced the phosphorylation and subsequent cleavage of Trop-2, followed by intracellular signaling by the resultant C-terminal fragment. Binding of β-catenin/transcription factor 4 (TCF4) along with the C-terminal fragment of Trop-2 to the ZEB1 promoter upregulated ZEB1 expression. Of note, siRNA-mediated knockdown of β-catenin and TCF4 increased the expression of E-cadherin through ZEB1 downregulation. Knockdown of Trop-2 in MCF-7 cells and DU145 cells resulted in downregulation of ZEB1 and subsequent upregulation of E-cadherin. Furthermore, wild-type and phosphomimetic Trop-2 but not phosphorylation-blocked Trop-2 were detected in the liver and/or lung of some nude mice bearing primary tumors inoculated intraperitoneally or subcutaneously with wild-type or mutated Trop-2 expressing cells, suggesting that Trop-2 phosphorylation, plays an important role in tumor cell mobility in vivo, too. Together with our previous finding of Trop-2 dependent regulation of claudin-7, we suggest that the Trop-2-mediated cascade involves concurrent derangement of both tight and adherence junctions, which may drive metastasis of epithelial tumor cells.

Targeting Trop-2 in cancer: Recent research progress and clinical application

The development of new antitumor drugs depends mainly upon targeting tumor cells precisely. Trophoblast surface antigen 2 (Trop-2) is a type I transmembrane glycoprotein involved in Ca2+ signaling in tumor cells. It is highly expressed in various tumor tissues than in normal tissues and represents a novel and promising molecular target for caner targeted therapy. Up to now, the mechanisms and functions associated with Trop-2 have been extensively studied in a variety of solid tumors. According to these findings, Trop-2 plays an important role in cell proliferation, apoptosis, cell adhesion, epithelial-mesenchymal transition, as well as tumorigenesis and tumor progression. In addition, Trop-2 related drugs are also being developed widely. There are a number of Trop-2 related ADC drugs that have demonstrated potent antitumor activity and are currently been studied, such as Sacituzumab Govitecan (SG) and Datopotamab Deruxtecan (Dato-Dxd). In this study, we reviewed the progress of Trop-2 research in solid tumors. We also sorted out the composition and rationale of Trop-2 related drugs and summarized the related clinical trials. Finally, we discussed the current status of Trop-2 research and expanded our perspectives on its future research directions. Importantly, we found that Trop-2 targeted ADCs have great potential for combination with other antitumor therapies. Trop-2 targeted ADCs can reprogramme tumor microenvironment through multiple signaling pathways, ultimately activating antitumor immunity.

Advances in Trop2-targeted therapy: Novel agents and opportunities beyond breast cancer

Trop2 is a transmembrane glycoprotein and calcium signal transducer with limited expression in normal human tissues. It is consistently overexpressed in a variety of malignant tumors and participates in several oncogenic signaling pathways that lead to tumor development, invasion, and metastasis. As a result, Trop2 has become an attractive therapeutic target in cancer treatment. The anti-Trop2 antibody-drug conjugate (Trodelvy™, sacituzumab govitecan) has been approved to treat metastatic triple-negative breast cancer. However, it is still unclear whether the success observed in Trop2-positive breast cancer could be replicated in other tumor types, owing to the differences in the expression levels and functions of Trop2 across cancer types. In this review, we summarize the recent progress on the structures and functions of Trop2 and highlight the potential diagnostic and therapeutic value of Trop2 beyond breast cancer. In addition, the promising novel Trop2-targeted agents in the clinic were discussed, which will likely alter the therapeutic landscape of Trop2-positive tumors in the future.

TROP2 (trophoblast cell-surface antigen 2): a drug target for breast cancer

INTRODUCTION

Breast cancer (BC) is the most common diagnosed cancer and the second leading cause of cancer-associated death in women, with the triple negative (TNBC) subtype being characterized by the poorest prognosis. New therapeutic targets are urgently needed to overcome the high metastatic potential, aggressiveness and poor survival of these tumors. Trop2 transmembrane glycoprotein, acting as an intracellular calcium signal transducer, recently emerged as a new potential target in epithelial cancers, in particular in breast cancer.

AREAS COVERED

We summarize the key features of Trop2 structure and function, describing the therapeutic strategies targeting this protein in cancer. Particular attention is paid to antibody-drug conjugates (ADCs), actually representing the most successful strategy.

EXPERT OPINION

ADCs targeting Trop2 recently received an accelerated FDA approval for the therapy of metastatic TNBC. The prospects for these novel ADCs in BC subtypes other than TNBC are discussed, taking into account the main pitfalls relative to Trop2 structure and function.

Alteration of Trop-2 expression in breast cancer cells by clinically used therapeutic agents and acquired tamoxifen resistance

Background

Sacituzumab govitecan is an antibody–drug conjugate that delivers SN-38, an active metabolite of irinotecan, to the target molecule, trophoblast cell-surface antigen 2 (Trop-2). It is a promising drug for triple-negative breast cancer and is anticipated to be effective for luminal breast cancer. The efficacy of the agent relies on the expression of Trop-2 rather than its intracellular function. However, conditions that alter the Trop-2 expression have not been well investigated.

Methods

We tested a range of clinically related treatments for their effect on Trop-2 expression in cultured breast cancer cell lines.

Results

The expression level of Trop-2 differed among cell lines, independent of their subtypes, and was highly variable on treatment with kinase inhibitors, tamoxifen, irradiation, and chemotherapeutic agents including irinotecan. While inhibitors of AKT, RSK, and p38 MAPK suppressed the Trop-2 expression, tamoxifen treatment significantly increased Trop-2 expression in luminal cancer cell lines. Notably, luminal cancer cells with acquired resistance to tamoxifen also exhibited higher levels of Trop-2. We identified transcription factor EB (TFEB) as a possible mechanism underlying tamoxifen-induced elevation of Trop-2 expression. Tamoxifen triggers dephosphorylation of TFEB, an active form of TFEB, and the effect of tamoxifen on Trop-2 was prevented by depletion of TFEB. A luciferase reporter assay showed that Trop-2 induction by TFEB was dependent on a tandem E-box motif within the Trop-2 promoter region.

Conclusions

Overall, these results suggest that the effectiveness of sacituzumab govitecan could be altered by concomitant treatment and that tamoxifen could be a favorable agent for combined therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12282-022-01389-3.

B7-H4 expression is upregulated by PKCδ activation and contributes to PKCδ-induced cell motility in colorectal cancer

Introduction

B7-H4 is overexpressed in colorectal cancer (CRC) and plays an important role in tumor growth and immunosuppression. However, the exact mechanism that regulates B7-H4 expression remains largely unknown. Here, we investigated whether protein kinase C δ (PKCδ) regulates the expression of B7-H4 in CRC.

Methods

By using immunohistochemical (IHC) and immunofluorescence (IF) staining, we analyzed the expression of B7-H4 and phospho-PKCδ (p-PKCδ) in 225 colorectal tumor samples and determined the clinical significance of the expression patterns. In vitro experiments were performed with the CRC cell lines HCT116 and SW620 to detect the effect of PKCδ activation on B7-H4 expression, and xenograft-bearing mice were treated with rottlerin to monitor the expression of B7-H4 and tumor metastasis.

Results

The B7-H4 expression level was significantly correlated with the p-PKCδ level (r = 0.378, P < 0.001) in tumor tissues. Coexpression of p-PKCδ and B7-H4 was significantly associated with moderate/poor differentiation (P = 0.024), lymph node metastasis (P = 0.001) and advanced Dukes’ stage (P = 0.002). Western blot analysis showed that Phorbol-12-Myristate-13-Acetate (TPA) increased B7-H4 expression in a concentration-dependent manner and that rottlerin abrogated the TPA-induced increase in B7-H4 expression. The protein levels of B7-H4 and p-STAT3 were significantly reduced by a PKCδ-specific siRNA. Moreover, the STAT3 inhibitor cryptotanshinone significantly decreased the B7-H4 protein level in CRC cells. Knockdown of B7-H4 or PKCδ suppressed cell migration and motility. Rottlerin also inhibited B7-H4 expression and tumor metastasis in vivo.

Conclusion

The B7-H4 expression level is significantly correlated with the p-PKCδ level and tumor metastasis in CRC samples. B7-H4 expression is upregulated by STAT3 activation via PKCδ and plays roles in PKCδ-induced cancer cell motility and metastasis, suggesting that the PKCδ/STAT3/B7-H4 axis may be a potential therapeutic target for CRC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02567-1.

TROP2 Expression in Sebaceous and Sweat Gland Carcinoma

Sebaceous carcinoma and sweat gland carcinoma (malignant tumors with apocrine and eccrine differentiation) are rare malignant skin adnexal tumors that differentiate toward sebaceous gland and eccrine and apocrine glands, respectively. Owing to the rarity of these carcinomas, standard treatments for advanced disease have not been established. Because the prognosis of patients with systemic metastasis is poor, a new treatment for these diseases is eagerly desired. Trophoblast cell surface antigen 2 (TROP2) and sacituzumab govitecan, an antibody–drug conjugate of TROP2, have attracted attention in the treatment of various solid tumors. In the current study, we immunohistochemically investigated TROP2 expression in 14 sebaceous carcinoma and 18 sweat gland carcinoma samples and found strong and relatively homogeneous TROP2 staining in both cancer types. The mean Histoscore, a semi-quantitative scoring ranging from 0 (negative) to 300, was 265.5 in sebaceous carcinoma and 260.0 in sweat gland carcinoma. These observations directly suggest that both sebaceous carcinoma and sweat gland carcinoma could be potentially treated with TROP2-targeted antibody–drug conjugates such as sacituzumab govitecan.

N-glycosylation status of Trop2 impacts its surface density, interaction with claudin-7 and exosomal release

Trophoblast antigen 2 (Trop2) is a type I transmembrane protein post-translationally modified by N-linked glycosylation. It was originally detected in trophoblasts but was later shown to be frequently overexpressed in many epithelial cancers. Recently, anti-Trop2 antibody-drug conjugate has been FDA approved for the treatment of metastatic triple-negative breast and urothelial carcinomas, making it an important tumor antigen. The current study explored the significance of N-glycosylation of Trop2 by substituting specific N-glycan addition sites by site-directed mutagenesis. The mutant proteins were characterized in transiently transfected HEK293 cells. The N-glycosylation mutants did not affect protein expression, stability, dimerization ability and matriptase mediated cleavage. However, N¹²⁰A and N²⁰⁸A mutants showed decreased interaction with its binding partner claudin-7. Our earlier reported Trop2 mutant V¹⁹⁴A, which shows aberrant glycosylation, also displayed hampered interaction with claudin-7. To further characterize the mutants, stable clones expressing wild type and mutant Trop2 were generated in OVCAR3 cell line. Interestingly, surface biotinylation assay showed significantly higher surface expression of N¹²⁰A and N²⁰⁸A mutants whereas surface localization was drastically reduced for V¹⁹⁴A Trop2 mutant. Though overexpression of wild type Trop2 did not cause any change in fibronectin-mediated FAK (Focal adhesion kinase) signaling; expression of N¹²⁰A mutant, surprisingly downregulated FAK signaling. Furthermore, exosomal release of Trop2 was also decreased in N¹²⁰A and N²⁰⁸A mutants. This data suggests that site-specific N-glycan addition determines Trop2 surface density, claudin-7 interaction and exosomal release.

Trop2 Expression in Extramammary Paget's Disease and Normal Skin

Extramammary Paget's disease (EMPD) is a rare skin cancer arising in the apocrine gland-rich areas. Most EMPD tumors are dormant, but metastatic lesions are associated with poor outcomes owing to the lack of effective systemic therapies. Trophoblast cell surface antigen 2 (Trop2), a surface glycoprotein, has drawn attention as a potential therapeutic target for solid tumors. Sacituzumab govitecan, an antibody-drug conjugate of Trop2, has recently entered clinical use for the treatment of various solid cancers. However, little is known about the role of Trop2 in EMPD. In this study, we immunohistochemically examined Trop2 expression in 116 EMPD tissue samples and 10 normal skin tissues. In normal skin, Trop2 was expressed in the epidermal keratinocytes, inner root sheaths, and infundibulum/isthmus epithelium of hair follicles, eccrine/apocrine glands, and sebaceous glands. Most EMPD tissues exhibited homogeneous and strong Trop2 expression, and high Trop2 expression was significantly associated with worse disease-free survival (p = 0.0343). These results suggest the potential use of Trop2-targeted therapy for EMPD and improve our understanding of the skin-related adverse effects of current Trop2-targeted therapies such as sacituzumab govitecan.

Clinicopathologic significance of TROP2 and phospho-TROP2 in gastric cancer

Trophoblast cell-surface antigen 2 (TROP2) is a transmembrane glycoprotein expressed in epithelial cells. Increased TROP2 expression has been reported to be associated with malignant progression in most carcinomas; however, TROP2 has a tumor-suppressive function in certain types of cancer. Since the function of TROP2 is controversial, the present study subsequently aimed to clarify the clinicopathologic significance of TROP2 and pTROP2 expression in human gastric cancer (GC). The cases of 704 patients with GC who underwent gastrectomy were retrospectively analyzed. The expression levels of TROP2 and pTROP2 in each tumor were evaluated by immunohistochemistry. The association between the clinicopathologic features of patients with GC and the levels of TROP2 and pTROP2 in their tumors was analyzed. Increased TROP2 and pTROP2 expression was identified in 330 (46.9%) and 306 (43.5%) of the 704 patients with GC, respectively. Increased TROP2 expression was associated with the histological intestinal type, high tumor invasion depth (T3/T4), lymph node metastasis, lymphatic invasion and venous invasion. By contrast, increased pTROP2 expression was associated with intestinal type, low tumor invasion depth (T1/2), no lymph node metastasis and no lymphatic invasion. Increased TROP2 expression was associated with poorer overall survival (OS) (P<0.01; log rank test), whereas increased pTROP2 expression was significantly associated with improved OS (P<0.01; log rank test). In conclusion, increased expression levels of TROP2, but not pTROP2, may be associated with the metastatic ability of GC, resulting in poor prognosis of patients with GC.

The role of Trop2 in prostate cancer: an oncogene, biomarker, and therapeutic target

Prostate cancer remains the second leading cause of cancer-associated deaths amongst American men. Trop2, a cell surface glycoprotein, correlates with poor clinical outcome and is highly expressed in metastatic, treatment-resistant prostate cancer. High levels of Trop2 are prognostic for biochemical recurrence. Trop2 regulates tumor growth and metastatic ability of prostate cancer. Moreover, overexpression of Trop2 drives the transdifferentiation to neuroendocrine phenotype in prostate cancer. In addition, Trop2 is overexpressed across epithelial cancers and has emerged as a promising therapeutic target in various solid epithelial cancers. The FDA (Food and Drug Administration) recently approved the use of a Trop2-targeting ADC (antibody-drug conjugate), Sacituzumab Govitecan (IMMU-132), for metastatic, triple-negative breast cancer with at least two prior therapies. Here, we review the role of Trop2 in prostate tumorigenesis and its potential as a promising biomarker and therapeutic target for prostate cancer.

PKCδ mediates mitochondrial ROS generation and oxidation of HSP60 to relieve RKIP inhibition on MAPK pathway for HCC progression

Both protein kinase C (PKC) and reactive oxygen species (ROS) are well-known signaling messengers cross-talking with each other to activate mitogen-activated protein kinases (MAPKs) for progression of hepatocellular carcinoma (HCC). However, the underlying mechanisms are not well elucidated. Especially, whether mitochondrial ROS (mtROS) is involved and how it triggers MAPK signaling are intriguing. In this study, we found mtROS generation and phosphorylation of MAPKs were mediated by PKCδ in HCCs treated with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Heat shock protein 60 (HSP60), one of the chaperones in mitochondria was the major protein oxidized in TPA-treated HCCs. Moreover, depletion of HSP60 or expression of HSP60 cysteine mutant prevented TPA-induced phosphorylation of MAPKs. To delineate how HSP60 mediated MAPK activation, the role of Raf kinase inhibitor protein (RKIP), a negative regulator of MAPK, was investigated. TPA dissociated RKIP from HSP60 in both mitochondria and cytosol, concurrently with translocation of HSP60 and MAPK from mitochondria to cytosol, which was associated with robust phosphorylation of MAPKs in the cytosol. Moreover, TPA induced opposite phenotypical changes of HCCs, G1 cell cycle arrest, and cell migration, which were prevented by mtROS scavengers and depletion of PKCδ and HSP60. Consistently, TPA increased the migration-related genes, hydrogen peroxide inducible clone5, matrix metalloproteinase-1/3, lamininγ2, and suppressed the cell cycle regulator cyclin E1 (CCNE1) via PKCδ/mtROS/HSP60/MAPK-axis. Finally, c-jun and c-fos were required for TPA-induced expression of the migration-related genes and a novel microRNA, miR-6134, was responsible for TPA-induced suppression of CCNE1. In conclusion, PKCδ cross-talked with mtROS to trigger HSP60 oxidation for release of RKIP to activate MAPK, regulating gene expression for migration, and G1 cell cycle arrest in HCC. Targeted therapy aiming at key players like PKCδ, RKIP, and HSP60 is promising for preventing HCC progression.

Trop2: Jack of All Trades, Master of None

Trophoblast cell surface antigen 2 (Trop2) is a widely expressed glycoprotein and an epithelial cell adhesion molecule (EpCAM) family member. Although initially identified as a transmembrane protein, other subcellular localizations and processed forms were described. Its congenital mutations cause a gelatinous drop-like corneal dystrophy, a disease characterized by loss of barrier function in corneal epithelial cells. Trop2 is considered a stem cell marker and its expression associates with regenerative capacity in various tissues. Trop2 overexpression was described in tumors of different origins; however, functional studies revealed both oncogenic and tumor suppressor roles. Nevertheless, therapeutic potential of Trop2 was recognized and clinical studies with drug-antibody conjugates have been initiated in various cancer types. One of these agents, sacituzumab govitecan, has been recently granted an accelerated approval for therapy of metastatic triple-negative breast cancer. In this article, we review the current knowledge about the yet controversial function of Trop2 in homeostasis and pathology.

EpCAM cellular functions in adhesion and migration, and potential impact on invasion: A critical review

EpCAM has long been known as a cell surface protein highly expressed in carcinomas. It has since become one of the key cancer biomarkers. Despite its high fame, its actual role in cancer development is still controversial. Beyond a flurry of correlative studies, which point either to a positive or a negative link with tumour progression, there has been surprisingly few studies on the actual cellular mechanisms of EpCAM and on their functional consequences. Clearly, EpCAM plays multiple important roles, in cell proliferation as well as in cell adhesion and migration. The two latter functions, directly relevant for metastasis, are the focus of this review. We attempt here to bring together the available experimental data to build a global coherent view of EpCAM functions. We also include in this overview EpCAM2/Trop2, the close relative of EpCAM. At the core of EpCAM (and EpCAM2/Trop2) function stands the ability to repress contractility of the actomyosin cell cortex. This activity appears to involve direct inhibition by EpCAM of members of the novel PKC family and of a specific downstream PKD-Erk cascade. We will discuss how this activity can result in a variety of adhesive and migratory phenotypes, thus potentially explaining at least part of the apparent inconsistencies between different studies. The picture remains fragmented, and we will highlight some of the conflicting evidence and the many unsolved issues, starting with the controversy around its original description as a cell-cell adhesion molecule.