Follicle-stimulating hormone promotes the growth of human epithelial ovarian cancer cells through the protein kinase C-mediated system

Astragalus polysaccharide ameliorates steroid-induced osteonecrosis of femoral head through miR-206/HIF-1α/BNIP3 axis

Declining autophagy and rising apoptosis are the main factors driving the development of steroid-induced osteonecrosis of the femoral head (SONFH). Here, we showed that astragalus polysaccharide (APS) improved femoral head necrosis via regulation of cell autophagy and apoptosis through microRNA (miR)-206/hypoxia inducible factor-1 (HIF-1α)/BCL2 interacting protein 3 (BNIP3) axis. The expression of miR-206, HIF-1α, and BNIP3 in SONFH specimens and cell model were measured using qPCR. SONFH cell model was treated with APS. Cell autophagy was evaluated using LC3-immunofluorescence assays. Flow cytometry was conducted to assess cell apoptosis. Apoptosis-related proteins and autophagy-related proteins were determined using western blot. Besides, dual-luciferase reporter assay was employed to investigate the relationship between miR-206 and HIF-1α. Here we showed that miR-206 expression was upregulated in SONFH tissues and cell model. APS promoted autophagy and inhibited apoptosis in SONFH cell model via downregulating miR-206. What is more, HIF-1α was the target of miR-206. Knockdown of HIF-1α reversed the recovery effect of miR-206 inhibitor on SONFH cell model. Furthermore, BNIP3 was the target of HIF-1α. HIF-1α overexpression promoted autophagy and inhibited apoptosis, and knockdown of BNIP3 abolished the recovery effect of HIF-1α overexpression in SONFH cell model. These results provided evidence that APS reduced miR-206 expression, and the downregulated miR-206 increased BNIP3 expression by targeting HIF-1α to promote autophagy and inhibit bone cell apoptosis. Our research proved that APS effectively improved SONFH by regulating cell autophagy and apoptosis.

The Role of Calcium Signaling in Regulation of Epithelial-Mesenchymal Transition

Despite substantial advances in the field of cancer therapeutics, metastasis is a significant challenge for a favorable clinical outcome. Epithelial to mesenchymal transition (EMT) is a process of acquiring increased motility, invasiveness, and therapeutic resistance by cancer cells for their sustained growth and survival. A plethora of intrinsic mechanisms and extrinsic microenvironmental factors drive the process of cancer metastasis. Calcium (Ca2+) signaling plays a critical role in dictating the adaptive metastatic cell behavior comprising of cell migration, invasion, angiogenesis, and intravasation. By modulating EMT, Ca2+ signaling can regulate the complexity and dynamics of events leading to metastasis. This review summarizes the role of Ca2+ signal remodeling in the regulation of EMT and metastasis in cancer.

Targeting Membrane Receptors of Ovarian Cancer Cells for Therapy

Ovarian cancer is a leading cause of death worldwide from gynecological malignancies, mainly because there are few early symptoms and the disease is generally diagnosed at an advanced stage. In addition, despite the effectiveness of cytoreductive surgery for ovarian cancer and the high response rates to chemotherapy, survival has improved little over the last 20 years. The management of patients with ovarian cancer also remains similar despite studies showing striking differences and heterogeneity among different subtypes. It is therefore clear that novel targeted therapeutics are urgently needed to improve clinical outcomes for ovarian cancer. To that end, several membrane receptors associated with pivotal cellular processes and often aberrantly overexpressed in ovarian cancer cells have emerged as potential targets for receptor-mediated therapeutic strategies including specific agents and multifunctional delivery systems based on ligand-receptor binding. This review focuses on the profiles and potentials of such strategies proposed for ovarian cancer treatment and imaging.

Luteinizing hormone inhibits cisplatin-induced apoptosis in human epithelial ovarian cancer cells

The elevation of Luteinizing hormone (LH) is commonly observed in epithelial ovarian cancer. This correlation suggests a causal relationship between LH and ovarian cancer. LH has been reported to inhibit apoptosis in ovarian cancer cells. Programmed cell death gene 6 (PDCD6), also known as apoptosis-linked gene-2, is an apoptotic mediator that is required for apoptosis to numerous death stimuli. Therefore, the aim of the present study was to determine whether PDCD6 may be induced by LH in ovarian cancer, and whether LH may affect the apoptosis through PDCD6. Flow cytometry was used to detect the effects of cisplatin on the induction of apoptosis by LH. PDCD6 expression was monitored by quantitative polymerase chain reaction and western blotting. The signaling transduction pathways were also investigated by western blotting. The present study demonstrated that LH reduced cisplatin-induced apoptosis in ovarian OVCAR-3 and SKOV-3 cancer cells. The results indicated that PDCD6 expression was inhibited by LH. In addition, the inhibition of PDCD6, induced by LH, was mediated through the activation of the phosphatidylinositol 3-kinase/protein kinase B and p44/42 mitogen-activated protein kinase transduction signaling pathways. The present results suggest that LH affects the sensitivity of ovarian cancer cells to chemotherapy, primarily by signaling to inhibit apoptosis and to additionally suppress PDCD6.

Gankyrin facilitates follicle-stimulating hormone-driven ovarian cancer cell proliferation through the PI3K/AKT/HIF-1α/cyclin D1 pathway

Gankyrin is a regulatory subunit of the 26kD proteasome complex. As a novel oncoprotein, gankyrin is expressed aberrantly in cancers from several different sites and has been shown to contribute to oncogenesis in endometrial and cervical carcinomas. Neither gankyrin's contribution to the development of epithelial ovarian cancer nor its interaction with follicle-stimulating hormone (FSH)-driven proliferation in ovarian cancer has been studied. Here we have found that gankyrin is overexpressed in ovarian cancers compared with benign ovarian cystadenomas and that gankyrin regulates FSH upregulation of cyclin D1. Importantly, gankyrin regulates PI3K/AKT signaling by downregulating PTEN. Prolonged AKT activation by FSH stimulation of the FSH receptor (FSHR) promotes gankyrin expression, which, in turn, enhances AKT activation by inhibiting PTEN. Overexpression of gankyrin decreases hypoxia inducible factor-1α (HIF-1α) protein levels, but has little effect on HIF-1α mRNA levels, which could be attributed to gankyrin mediating HIF-1α protein stability via the ubiquitin-proteasome pathway. Reduction in HIF-1α protein stability led to attenuation of the binding with cyclin D1 promoter, resulted in abolishment of the negative regulation of cyclin D1 by HIF-1α, which promotes proliferation of ovarian cancer cells. Our results document that gankyrin regulates HIF-1α protein stability and cyclin D1 expression, ultimately mediating FSH-driven ovarian cancer cell proliferation.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Gonadotropin signalling in epithelial ovarian cancer

Ovarian cancer is the most lethal of all gynecologic malignancies, although its aetiology remains poorly understood. A role for the gonadotropins, follicle-stimulating hormone (FSH) and luteinising hormone (LH), has been implicated in a variety of different aspects of ovarian cancer tumorigenesis, including cellular proliferation, migration and invasion. This review focuses on the latest advances in knowledge concerning signalling pathways and functional consequences of gonadotropin action, including changes in protein-, miRNA- and gene expression, in epithelial ovarian cancer cells.

FSH stimulates expression of the embryonic gene HMGA2 by downregulating let-7 in normal fimbrial epithelial cells of ovarian high-grade serous carcinomas

FSH may increase the risk of ovarian malignancy and play a key role in ovarian carcinogenesis, although the mechanism(s) are undefined. HMGA2 overexpression has been observed to be an early genetic event in tumorigenesis. The present study was designed to investigate the effect of FSH on let-7, HMGA2 and p53 expression in normal fimbrial epithelial cells of ovarian high-grade serous carcinomas (HGSCs). A primary human Fallopian tube (FT) fimbrial epithelium ex vivo culture system of low-grade serous carcinomas (LGSCs) and HGSCs was established. The levels of HMGA2, let-7, p53 and FSHR were evaluated by western blotting and reverse transcription (RT)-PCR. Treatment with FSH significantly increased HMGA2 expression in a time-dependent manner and the let-7 expression levels decreased gradually over time in the normal fimbrial epithelial cells of HGSCs. However, we did not observe similar results in LGSCs. In addition, knockdown of let-7 suppressed HMGA2 expression. p53 was not detected in the normal fimbrial epithelial cells before or after FSH administration. Our results indicate that FSH increases the expression of HMGA2 by downregulating the expression of let-7 in normal fimbrial epithelial cells of HGSCs, but no occurrence of p53 mutation. The susceptibility of fimbria to FSH in HGSCs compared with those in LGSCs is different.

Effects of the FSH receptor gene polymorphism p.N680S on cAMP and steroid production in cultured primary human granulosa cells

The study was designed to evaluate in vitro the cellular mechanisms of the single nucleotide polymorphism (SNP) p.N680S of the FSH receptor gene (FSHR) in human granulosa cells (GC) and included patients homozygous for the FSHR SNP (NN/SS) undergoing ovarian stimulation. GC were isolated during oocyte retrieval and cultured for 1–7 days. Basal oestradiol and progesterone concentrations were measured after short-term culture. The kinetics of cAMP, oestradiol and progesterone concentrations in response to various amounts of FSH were analysed in a 6–7 day culture. Basal oestradiol, but not progesterone, concentrations on day 1 of GC culture, were significantly higher in NN compared with SS (P = 0.045), but non-responsive to FSH stimulation. Immunofluorescence microscopy demonstrated the re-appearance of FSHR expression with increasing days in culture. Upon stimulation with FSH, GC cultured for 6–7 days displayed a dose-dependent increase of cAMP, oestradiol and progesterone but no difference in the EC50 values between both variants. Primary long-term GC cultures are a suitable system to study the effects of FSH in vitro. However, the experiments suggest that factors down-stream of progesterone production or external to GC might be involved in the clinically observed differences in an FSHR variant-mediated response to FSH.

Follicle-stimulating hormone promotes proliferation of cultured chicken ovarian germ cells through protein kinases A and C activation

The study was conducted to investigate the effects of follicle-stimulating hormone (FSH) on embryonic chicken ovarian germ cell proliferation and its possible involvements of protein kinases A (PKA) and C (PKC) pathways. Ovarian cells were treated with FSH alone or in the presence of forskolin (FRSK), PKA inhibitor (H(89)), PKC activator (PMA) or inhibitor (H(7)). The germ cell number was counted from micropictures. The immunocytochemistry of proliferating cell nuclear antigen (PCNA) was applied to identify the proliferating cells. The germ cell labeling index (LI) was determined for cell proliferation. The FSH treatment increased the germ cell number, and this stimulating effect was enhanced by FRSK or PMA, but inhibited by H(89) or H(7) in a dose-dependent manner. Moreover, the PCNA-LI showed parallel changes with germ cell numbers. This study suggests that FSH may stimulate proliferation of cultured chicken ovarian germ cells by activation of both the PKA and PKC signaling pathways.

Are gonadotrophins tumorigenic--a critical review of clinical and experimental data

The growth of many gonadal and extragonadal tumors is stimulated by gonadal sex hormones. Because gonadal hormone production is regulated by pituitary gonadotrophins, the latter hormones can be considered as indirect tumor promoters. In addition, there is a growing body of evidence that both gonadal (e.g. ovarian cancer) and extragonadal (e.g. breast, uterus, prostate and adrenal) tumors express gonadotrophin receptors, indicating the possibility of a direct tumorigenic role for FSH and LH. The purpose of this brief review is to present a critical evaluation of the current information, both clinical and experimental, about the direct involvement of gonadotrophins in the induction and growth of gonadal and extragonadal tumors.

Overexpression of follicle-stimulating hormone receptor facilitates the development of ovarian epithelial cancer

We previously showed that the expressing level of FSH receptor (FSHR) increased from ovarian epithelial inclusions (OEIs) to benign ovarian epithelial tumors (OETs) and to borderline OETs, whereas FSHR levels decreased with an increase in carcinoma grade. The aim of this study was to investigate the role of FSHR in OET development. MCV152 cells with FSHR overexpression showed an increased cellular proliferation and invasive capacity, which was associated with reduced levels of prohibitin and RII-beta expression and increased levels of HER-2/neu, c-Myc, and EGFR expression. Overexpression of FSHR may be associated with an elevated level of OET cell proliferation via an enhanced activity of potential oncogenic pathways. Therefore, the findings in this study suggest that overexpression of FSHR may play a role in OET development.

Effects of pre-mating nutrition on mRNA levels of developmentally relevant genes in sheep oocytes and granulosa cells

The present study was designed to investigate the relationship between pre-mating nutrition and the relative amounts of a panel of developmentally relevant genes in ovine oocytes and granulosa cells. Cast age ewes were fed a ration providing 0.5x (0.5 M) or 1.5x (1.5 M) live weight maintenance requirements for 2 weeks before slaughter. The ewes were synchronized and superovulated with FSH and pregnant mares serum gonadotropin. At slaughter, oocytes and granulosa cells were aspirated from follicles >2 mm in diameter and the relative abundance of 8 and 17 transcripts in oocytes and granulosa cells respectively were analyzed by semi-quantitative RT-PCR. In the oocytes, no differences between groups were observed for five transcripts (GDF9, BMP15, c-kit, glucose transporter 1 (SLC2A1), and hexokinase 1), but a lower amount of glucose transporter 3 (SLC2A3), sodium/glucose cotransporter 1 (SLC5A1), and Na(+)/K(+) ATPase mRNAs was detected in the 0.5 M group. Increased expression of PTGS2, HAS2, and the leptin receptor long form was observed in granulosa cells from the 0.5 M group. No differences between groups were observed for the other transcripts (early growth response factor-1, estrogen receptor-alpha, LH and FSH receptors, gremlin 1, pentraxin 3, KIT ligand, glucose transporters 1, 3, and 8, IGF1, IGF1 receptor, leptin receptor, and tumor necrosis factor-stimulated gene 6). Expression of leptin and sodium/glucose cotransporter 1 was not detected in both groups. The present data indicate that pre-mating nutrition is associated with alteration in the mRNA content in oocytes and surrounding follicle cells in ewes, which may account for the reduced reproductive performance typical of ewes that are fed a restricted ration for a short period of time before mating.

Polymorphism of the FSH receptor and ovarian response to FSH

Follicle-stimulating hormone (FSH) is a key factor in human reproduction. FSH activates its receptor (FSHR) located exclusively on Sertoli cells in the testis and granulosa cells in the ovary. Two common single nucleotide polymorphisms (SNP) within exon 10 of the human FSHR gene result in two almost equally common allelic variants exhibiting threonine (Thr) or alanine (Ala) at position 307 in the hinge region, respectively, asparagine (Asn) or serine (Ser) at codon 680 of the intracellular domain. Clinical studies have demonstrated that p.N680S polymorphism determines the ovarian response to FSH stimulation in patients undergoing IVF-treatment. Patients with the Ser(680) allele need more FSH during the stimulation phase to reach the serum estradiol levels of Asn(680) patients. A study investigating women with normal, mono-ovulatory menstrual cycles revealed that the Ser(680)/Ser(680) genotype leads to higher FSH serum levels and a prolonged cycle. To date, the molecular mechanism underlying the partial "resistance" of the Ser(680)-FSHR to FSH remains unclear. Future experiments should extend our current understanding of FSH action on follicular selection and dominance, thereby permitting novel, patient-tailored therapies for infertility and fertility preservation.

Gonadotropins and ovarian cancer

Ovarian epithelial cancer (OEC) accounts for 90% of all ovarian cancers and is the leading cause of death from gynecological cancers in North America and Europe. Despite its clinical significance, the factors that regulate the development and progression of ovarian cancer are among the least understood of all major human malignancies. The two gonadotropins, FSH and LH, are key regulators of ovarian cell functions, and the potential role of gonadotropins in the pathogenesis of ovarian cancer is suggested. Ovarian carcinomas have been found to express specific receptors for gonadotropins. The presence of gonadotropins in ovarian tumor fluid suggests the importance of these factors in the transformation and progression of ovarian cancers as well as being prognostic indicators. Functionally, there is evidence showing a direct action of gonadotropins on ovarian tumor cell growth. This review summarizes the key findings and recent advances in our understanding of these peptide hormones in ovarian cancer development and progression and their role in potential future cancer therapy. We will first discuss the supporting evidence and controversies in the "gonadotropin theory" and the use of animal models for exploring the involvement of gonadotropins in the etiology of ovarian cancer. The role of gonadotropins in regulating the proliferation, survival, and metastasis of OEC is next summarized. Relevant data from ovarian surface epithelium, which is widely believed to be the precursor of OEC, are also described. Finally, we will discuss the clinical applications of gonadotropins in ovarian cancer and the recent progress in drug development.

Hormonal therapy in ovarian cancer

Ovarian carcinoma continues to be the leading cause of death due to gynecological malignancy. Epidemiologic studies indicate that steroid hormones play roles in ovarian carcinogenesis. Gonadotropins, estrogen, and androgen may be causative factors, while gonadotropin-releasing hormone and progesterone may be protective factors in ovarian cancer pathogenesis. Experimental studies have shown that hormonal receptors are expressed in ovarian cancer cells and mediate the growth-stimulatory or growth-inhibitory effects of the hormones on these cells. Hormonal therapeutic agents have been evaluated in several clinical trials. Most of these trials were conducted in patients with recurrent or refractory ovarian cancer, with modest efficacy and few side effects. Better understanding of the mechanisms through which hormones affect cell growth may improve the efficacy of hormonal therapy. Molecular markers that can reliably predict major clinical outcomes should be investigated further in well-designed trials.

Endocrine signaling in ovarian surface epithelium and cancer

Ovarian cancer is the sixth most common cancer and the fifth leading cause of cancer-related death among women in developed countries. Greater than 85% of human ovarian cancer arises within the ovarian surface epithelium (OSE), with the remainder derived from granulosa cells or, rarely, stroma or germ cells. The pathophysiology of ovarian cancer is the least understood among all major human malignancies because of a poor understanding of the aetiological factors and mechanisms of ovarian cancer progression. There is increasing evidence suggesting that several key reproductive hormones, such as GnRH, gonadotrophins and sex steroids, regulate the growth of normal OSE and ovarian cancer cells. The objective of this review was to highlight the effects of these endocrine factors on ovarian cancer cell growth and to summarize the signalling mechanisms involved in normal human OSE and its neoplastic counterparts.

Gonadotropins activate proteolysis and increase invasion through protein kinase A and phosphatidylinositol 3-kinase pathways in human epithelial ovarian cancer cells

Despite evidence that gonadotropins may facilitate peritoneal metastasis of ovarian cancer by increasing cell adhesion, the action and molecular mechanism of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in ovarian cancer invasion is not well characterized. In the present study, we investigated the effects of FSH and LH on the invasive activity and the expression of metastasis-related proteinases in human epithelial ovarian cancer by Western blot, zymography, reverse transcription-PCR (RT-PCR), ELISA, and Boyden chamber assay. Treatment with FSH or LH (10, 100, or 1,000 ng/mL) significantly increased the invasion of ovarian cancer cell lines, including BG-1, CaOV-3, and SKOV-3 cells but not OVCAR-3 cells. In addition, treatment of SKOV-3 cells with FSH or LH (100 or 1,000 ng/mL) enhanced the expression and activation of matrix metalloproteinases (MMP-2 and MMP-9) as shown by RT-PCR, gelatin zymography, and ELISA. Pretreatment with [(2R)-2-(hydroxamido-carbonylmethyl)-4-methylpentanoyl]-l-tryptophan methylamide (10 micromol/L), a total MMP inhibitor, and 3-(4-phenoxyphenylsulfonyl)-propylthiirane (20 micromol/L), a specific gelatinase inhibitor, neutralized the proinvasive effect of gonadotropins in SKOV-3 cells. In addition, the secretion of tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and plasminogen activator inhibitor-1 was significantly decreased by FSH and LH (100 or 1,000 ng/mL). We further showed that gonadotropins induced an increase in SKOV-3 invasiveness via the activation of protein kinase A (PKA) and phosphatidylinositol 3-kinase (PI3K) signaling pathways. Taken together, these results suggest that gonadotropins may contribute to ovarian cancer metastasis via activation of proteolysis and increase in invasion through the PKA and PI3K pathways.

Does hormone replacement therapy prevent epithelial ovarian cancer?

Two much-debated hypotheses regarding the aetiology of epithelial ovarian cancer (EOC) are incessant ovulation and gonadotrophin stimulation. A significant inverse correlation is found between the risk of EOC and number of pregnancies, duration of oral contraceptive use (about 10% risk reduction per year) and duration of breastfeeding. Whereas ovulation in the 20-29 year age group was associated with a 20% increase in risk for each year of ovulation, maximum protective effect was noticed in late childbirth (>35 years). Although both in-vitro and in-vivo studies showed that gonadotrophins may initiate and stimulate the growth of EOC, it is not known whether gonadotrophins promote EOC. FSH and LH receptors have been detected by ligand-binding assay and by reverse transcriptase polymerase chain reaction in ovarian surface epithelium (OSE) and in malignant epithelial ovarian tissue. Key aetiological events for this cancer may occur in the premenopausal period. Although hormone replacement therapy (HRT) can lower FSH and LH concentrations substantially, it cannot reduce EOC. The ideal time of ovulation and/or gonadotrophin suppression for prevention of EOC, and why oral contraceptives (OC) can but HRT cannot reduce EOC effectively, are unknown. Various growth-related genes, factors, adhesion molecules and angiogenic factors are present in OSE. Pituitary ovarian axis hormones seem to maintain a delicate balance towards growth control whilst the resultant chain of abnormal growth-promoting events occur at cellular level. Reports regarding the relation of exogenous and endogenous hormones, especially oestrogen, and post-menopausal EOC are reviewed.

Genetic complexity of FSH receptor function

The interaction between follicle-stimulating hormone (FSH) and the FSH receptor (FSHR) is essential for normal oogenesis and spermatogenesis. Recently, single-nucleotide polymorphisms (SNPs) have been assigned to the FSHR gene. These give rise to different FSHR haplotypes that modify the action of FSH. In women, FSH sensitivities during the menstrual cycle and different cycle lengths are observed, depending on the FSHR haplotype. Thus, SNPs of the FSHR determine the ovarian response and should, therefore, be considered in controlled ovarian hyperstimulation during assisted-reproduction techniques in women with normal ovarian function. In men, the impact of the FSHR SNPs is unclear. The genetic complexity of FSHR should be considered when studying FSH action. These SNPs are one of the first examples in which genetic changes contribute to fine-tuning the endocrine regulation of reproduction. A rational pharmacogenetic approach that combines FSH dose according to the FSHR haplotype is envisaged.

Gonadotropin (LH, FSH) levels in serum and cyst fluid in epithelial tumors of the ovary

OBJECTIVES

The aim of this work was to determine gonadotropin (LH, FSH) levels in serum and cyst fluid in various type of ovarian epithelial neoplasms (benign, borderline, malignant) and to compare them with levels in benign cysts. Additionally we decided to estimate if there were some significant correlations between serum and ovarian cyst fluid in gonadotropin levels in all investigated groups.

MATERIALS AND METHODS

The study group included 74 patients before (n=36) and after (n=38) menopause, divided into four groups depending on the histopathologic diagnosis. Serum and cyst fluid levels of LH and FSH were determined in all patients.

RESULTS

We found statistically significant differences concerning LH and FSH levels in serum and cyst fluid between malignant and borderline tumors, between malignant tumors and benign cystadenomas and between malignant tumors and non-neoplastic cysts. We also found statistically significant correlations between serum and cyst fluid as to FSH and LH levels in patients with borderline tumors. There were no statistically significant correlations between serum and cyst fluid as to FSH and LH levels in patients with malignant epithelial tumors (group 1) and in patients with benign cystadenomas (group 3).

CONCLUSIONS

High FSH and LH levels in cyst fluid of malignant epithelial tumors of the ovary are in line with the gonadotropin theory of tumor growth. Simultaneous determination of various types inhibin levels appears to be an interesting topic for our future research.

Protein kinase C alpha expression in breast and ovarian cancer

In recent years research has focused on the development of specific, targeted drugs to treat cancer. One approach has been to block intracellular signaling proteins, such as protein kinase C alpha (PKC-alpha). To help support the rationale for clinical studies of a PKC-alpha-targeted therapy in breast and ovarian cancers, we reviewed publications studying PKC-alpha expression in these tumors. Since these investigations were mostly performed in cell lines, we supplemented this review with some preliminary findings from studies examining PKC-alpha expression in tumor tissue biopsies obtained from patients with breast and ovarian cancer. Based on the reviewed publications using representative cell lines and our preliminary findings on tumor tissue of patients with breast cancer, we infer that PKC-alpha levels may especially be increased in breast cancer patients with low or negative estrogen receptor (ER) levels. Thus, clinical studies determining efficacy of selective or specific inhibitors of PKC-alpha should include determination of ER status in order to help answer whether blocking PKC-alpha in patients with low or absent ER can result in clinical benefit.