Neratinib + fulvestrant + trastuzumab for HR-positive, HER2-negative, HER2-mutant metastatic breast cancer: outcomes and biomarker analysis from the SUMMIT trial

BACKGROUND

HER2 mutations are targetable alterations in patients with hormone receptor-positive (HR+) metastatic breast cancer (MBC). In the SUMMIT basket study, patients with HER2-mutant MBC received neratinib monotherapy, neratinib + fulvestrant, or neratinib + fulvestrant + trastuzumab (N + F + T). We report results from 71 patients with HR+, HER2-mutant MBC, including 21 (seven in each arm) from a randomized substudy of fulvestrant versus fulvestrant + trastuzumab (F + T) versus N + F + T.

PATIENTS AND METHODS

Patients with HR+ HER2-negative MBC with activating HER2 mutation(s) and prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) therapy received N + F + T (oral neratinib 240 mg/day with loperamide prophylaxis, intramuscular fulvestrant 500 mg on days 1, 15, and 29 of cycle 1 then q4w, intravenous trastuzumab 8 mg/kg then 6 mg/kg q3w) or F + T or fulvestrant alone. Those whose disease progressed on F + T or fulvestrant could cross-over to N + F + T. Efficacy endpoints included investigator-assessed objective response rate (ORR), clinical benefit rate (RECIST v1.1), duration of response, and progression-free survival (PFS). Plasma and/or formalin-fixed paraffin-embedded tissue samples were collected at baseline; plasma was collected during and at end of treatment. Extracted DNA was analyzed by next-generation sequencing.

RESULTS

ORR for 57 N + F + T-treated patients was 39% [95% confidence interval (CI) 26% to 52%); median PFS was 8.3 months (95% CI 6.0-15.1 months). No responses occurred in fulvestrant- or F + T-treated patients; responses in patients crossing over to N + F + T supported the requirement for neratinib in the triplet. Responses were observed in patients with ductal and lobular histology, 1 or ≥1 HER2 mutations, and co-occurring HER3 mutations. Longitudinal circulating tumor DNA sequencing revealed acquisition of additional HER2 alterations, and mutations in genes including PIK3CA, enabling further precision targeting and possible re-response.

CONCLUSIONS

The benefit of N + F + T for HR+ HER2-mutant MBC after progression on CDK4/6is is clinically meaningful and, based on this study, N + F + T has been included in the National Comprehensive Cancer Network treatment guidelines. SUMMIT has improved our understanding of the translational implications of targeting HER2 mutations with neratinib-based therapy.

Tumor Cell-Intrinsic PD-L1 Effects on Radiation-Induced Locoregional Antitumor Immunity

PURPOSE/OBJECTIVE(S)

Targeting PD-L1 is a beneficial strategy to reinvigorate antitumor immunity, however variable response and resistance are challenging and suggest the need for multimodality approaches. Tumor cell-intrinsic PD-L1 signals also regulate non-canonical pathogenic pathways that may impact treatment resistance. Ionizing radiation (IR) can induce antitumor immunity and has demonstrated therapeutic synergy with immunotherapy in some cases, however tumor-driven immunologic mechanisms affecting clinical outcomes remain incompletely understood. In this study, we investigated the impact of tumor cell-intrinsic PD-L1 signals on IR-induced locoregional immune response and tumor control.

MATERIALS/METHODS

We used orthotopic B16-F10 melanoma (WT-B16) and 4T1 triple negative breast cancer (WT-4T1) murine tumor models, as well as PD-L1 disabled variants (KO) generated by CRISPR/Cas9, implanted bilaterally. IR (10 Gy) was targeted at one tumor alone to evaluate both direct and indirect IR effects based on tumor PD-L1 status. We evaluated response by tumor volume (TV) measurements, flow cytometry of tumor-infiltrating lymphocytes (TILs) and tumor draining lymph nodes (TDLNs) in both irradiated and unirradiated compartments, and granzyme B (GZB) PET imaging to assess functional in vivo changes. Chemokine-based multiplex assays were used to assess cell lines receiving IR (4Gy) and ex vivo tumor lysates and serum.

RESULTS

IR-induced local tumor control was not significantly affected based on tumor PD-L1 status, however deactivation of tumor cell PD-L1 enhanced IR-induced regional tumor control. Unirradiated WT tumors in mice harboring irradiated KO but not irradiated WT tumors demonstrated a significant mean reduction in TV with instances of complete distant tumor regression. PET imaging demonstrated a nearly 2-fold higher concentration of GZB in KO versus WT tumors, in line with known locally immunosuppressive effects of tumor PD-L1. Remarkably, GZB levels were >1.5-fold higher in unirradiated WT tumors in mice harboring an irradiated KO versus WT tumor, which correlated with a 50% increase in PD-1+CD8+ T cells. Higher levels of CD62+CD44- naïve CD4+ (4-fold) and CD8+ (2-fold) memory T cells were seen in TDLNs of irradiated KO versus WT tumors. Cytokine levels positively correlated with immune recruitment and activation status, as CXCL10, CCL2 and CCL5 were significantly upregulated in PD-L1 KO versus WT tumors cells.

CONCLUSION

Results from this study demonstrate cell-intrinsic PD-L1 inhibits IR-induced locoregional immune activation and frequency of regional tumor control, with clinical implications including therapeutic targeting of tumor cell-intrinsic PD-L1 signals to enhance IR-induced immunogenicity, utility of IR based on tumor PD-L1 status particularly in the metastatic setting, and immunotherapy combinations. Future studies investigating mechanisms of resistance to IR-induced immune activation to enhance responsiveness are warranted.

Evaluation of immunologic parameters in canine glioma patients treated with an oncolytic herpes virus

AIM

To molecularly characterize the tumor microenvironment and evaluate immunologic parameters in canine glioma patients before and after treatment with oncolytic human IL-12-expressing herpes simplex virus (M032) and in treatment naïve canine gliomas.

METHODS

We assessed pet dogs with sporadically occurring gliomas enrolled in Stage 1 of a veterinary clinical trial that was designed to establish the safety of intratumoral oncoviral therapy with M032, a genetically modified oncolytic herpes simplex virus. Specimens from dogs in the trial and dogs not enrolled in the trial were evaluated with immunohistochemistry, NanoString, Luminex cytokine profiling, and multi-parameter flow cytometry.

RESULTS

Treatment-naive canine glioma microenvironment had enrichment of Iba1 positive macrophages and minimal numbers of T and B cells, consistent with previous studies identifying these tumors as immunologically "cold". NanoString mRNA profiling revealed enrichment for tumor intrinsic pathways consistent with suppression of tumor-specific immunity and support of tumor progression. Oncolytic viral treatment induced an intratumoral mRNA transcription signature of tumor-specific immune responses in 83% (5/6) of canine glioma patients. Changes included mRNA signatures corresponding with interferon signaling, lymphoid and myeloid cell activation, recruitment, and T and B cell immunity. Multiplexed protein analysis identified a subset of oligodendroglioma subjects with increased concentrations of IL-2, IL-7, IL-6, IL-10, IL-15, TNFα, GM-CSF between 14 and 28 days after treatment, with evidence of CD4⁺ T cell activation and modulation of IL-4 and IFNγ production in CD4⁺ and CD8⁺ T cells isolated from peripheral blood.

CONCLUSION

These findings indicate that M032 modulates the tumor-immune microenvironment in the canine glioma model.

The BET bromodomain inhibitor JQ1 suppresses growth of pancreatic ductal adenocarcinoma in patient-derived xenograft models

The primary aim of this study was to evaluate the antitumor efficacy of the bromodomain inhibitor JQ1 in pancreatic ductal adenocarcinoma (PDAC) patient-derived xenograft (tumorgraft) models. A secondary aim of the study was to evaluate whether JQ1 decreases expression of the oncogene c-Myc in PDAC tumors, as has been reported for other tumor types. We used five PDAC tumorgraft models that retain specific characteristics of tumors of origin to evaluate the antitumor efficacy of JQ1. Tumor-bearing mice were treated with JQ1 (50 mg/kg daily for 21 or 28 days). Expression analyses were performed with tumors harvested from host mice after treatment with JQ1 or vehicle control. An nCounter PanCancer Pathways Panel (NanoString Technologies) of 230 cancer-related genes was used to identify gene products affected by JQ1. Quantitative RT-PCR, immunohistochemistry and immunoblots were carried out to confirm that changes in RNA expression reflected changes in protein expression. JQ1 inhibited the growth of all five tumorgraft models (P<0.05), each of which harbors a KRAS mutation; but induced no consistent change in expression of c-Myc protein. Expression profiling identified CDC25B, a regulator of cell cycle progression, as one of the three RNA species (TIMP3, LMO2 and CDC25B) downregulated by JQ1 (P<0.05). Inhibition of tumor progression was more closely related to decreased expression of nuclear CDC25B than to changes in c-Myc expression. JQ1 and other agents that inhibit the function of proteins with bromodomains merit further investigation for treating PDAC tumors. Work is ongoing in our laboratory to identify effective drug combinations that include JQ1.

Magneto-Transport Measurements on Si/Si1−xGex Resonant Tunneling Structures

We have investigated magneto-transport properties of differently strained Si/ Si1−xGex resonant tunneling devices. The built-in strain was either put in the Si layers, by means of a thick., relaxed Si1−xGex buffer layer, or in the Si1−xGex layers, in which case all Si1−xGex layers were grown below the critical thickness, and a Si1−xGex spacer layer with graded Ge content was used. Magnetic fields parallel to the interface have been employed to probe the in-plane dispersion in the quantum well. This is used to study the effect of band-mixing in the two strain configurations. A field perpendicular to the interface resolves some Landau level splitting. Most strikingly, however, is the similarity in the spectra with the case when the magnetic field is applied parallel to the interfaces. This indicates broadening of the levels, possibly due to scattering, and the importance of 3-dimensional band structure effects.

Body site colonization in patients with community-associated methicillin-resistant Staphylococcus aureus and other types of S. aureus skin infections

Efforts to control spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are often based on eradication of colonization. However, the role of nasal and non-nasal colonization in the pathogenesis of these infections remains poorly understood. Patients with acute S. aureus skin and soft tissue infection (SSTI) were prospectively enrolled. Each subject's nasal, axillary, inguinal and rectal areas were swabbed for S. aureus and epidemiological risk factors were surveyed. Among the 117 patients enrolled, there were 99 patients who had an SSTI and for whom data could be analysed. Sixty-five patients had a CA-MRSA SSTI. Among these patients, MRSA colonization in the nares, axilla, inguinal area and rectum was 25, 6, 11 and 13%, respectively, and 37% overall were MRSA colonized. Most (96%) MRSA colonization was detected using nose and inguinal screening alone. Non-nasal colonization was 25% among CA-MRSA patients, but only 6% among patients with CA-methicillin-susceptible S. aureus (MSSA) or healthcare-associated MRSA or MSSA. These findings suggest that colonization patterns in CA-MRSA infection are distinct from those in non-CA-MRSA S. aureus infections. The relatively high prevalence of non-nasal colonization may play a key role in CA-MRSA transmission and acquisition of infection.

A study of femoral artery by twin drivers in magnetic resonance interference elastography

Magnetic Resonance Elastography (MRE) is a phase-contrast technique using conventional Magnetic Resonance Imaging system to visualize propagating shear waves and study the stiffness of tissues. Usually, shear vibrations are applied to the surface of tissues by means of mechanical driver at one point. But in femoral artery study, the shear wave generated by the single driver on the surface of thigh cannot reach the femoral artery behind vein because of the blockage from the vein. In this study, the twin drivers set developed in our laboratory is used to overcome the problem. By using twin drivers driven simultaneously, interference shear wave pattern is generated. MR Interference Elastography is using interference shear wave image to study the stiffness of tissues. And, a finite element modeling was used to simulate single and twin driver datasets. The method was applied to in vivo human's femoral artery. And the result demonstrates the feasibility of this method. Further study will be conducted with the twin drivers in more in-vivo studies.

In vivo tumor detection on rabbit with biopsy needle as MRE driver

Magnetic Resonance Elastography (MRE) is a phase contrast imaging technique to quantitatively measure the elasticity of tissues. Typically, the oscillating driver is placed on the surface of objects to generate shear waves. When it is applied to detect tumors in deep location, the depth penetration of the wave is limited by attenuation and the biopsy procedure has to be performed separately. In this study, we describe a method using biopsy needle as the MRE driver to produce shear waves in tissues. We made comparison between the MRE acquisitions obtained with biopsy needle and surface drivers. Because the well-defined propagation wave pattern reduces the error in wavelength calculation, the acquisitions of biopsy needle driver shows better homogeneity in stiffness map. We also performed the experiment with the biopsy needle for in vivo tumor detection in rabbits. This study demonstrates that the biopsy needle driver is more effective than the surface driver for accurately measuring the stiffness and location of the tumor.

Biopsy needle as MRE driver for tumor detection

Magnetic Resonance Elastography (MRE) is a phase contrast imaging technique to quantitatively measure the elasticity of tissues. Typically, an oscillating driver is placed on the surface to generate the shear waves. The depth penetration of the wave is limited by attenuation and the biopsy procedure has to be done separately. In this study, we use a biopsy needle as the driver to detect the 15% porcine gel inclusion in a 10% porcine gel phantom which simulates a tumor in tissues. We also perform the experiment with the biopsy needle for in-vivo tumor detection in rabbits. It is shown that the biopsy needle driver can accurately measure the stiffness and location of the tumor.

Shear waves induced by moving needle in MR elastography

Magnetic resonance elastography (MRE) is a phase contrast-based method for observing shear wave propagation in a material to determine its stiffness. The objective of this study was to determine whether shear waves suitable for MRE could be induced using a moving acupuncture needle. Tissue-simulating bovine gel phantom and a 0.4 mm diameter acupuncture needle were used in the experiment. The results showed that observable shear waves could be induced in the gel phantom by cyclic needle motion. The observed wavelength varied with excitation frequency, as expected. Generating shear waves using moving needles may be a useful tool to study the basic mechanism of acupuncture with MRE. Further study will be conducted to observe the wave motion in inhomogeneous media and acupuncture-induced effects in in-vivo studies.

Myocardial Fiber Length Mapping with MR Diffusion Tensor Imaging

Diffusion tensor MRI is emerging as a rapid, nondestructive method to map myocardial fiber organization. A precise biological description of myocardial fiber performance requires knowledge of four variables: length, force, velocity and time. However, study of quantification of myocardial fiber length is lacking. The current study aims to show myocardial fiber length maps of formalin-fixed heats. Diffusion tensor MRI with medium diffusion resolution (15 directions) was performed in one isolated pig heart. Fiber length maps were investigated in multiple short-axis slices. The results provide supplementary information of myocardial fiber organization. To our knowledge, the present study is the first report of the myocardial fiber length mapping.

Antioxidant enzyme inhibitors enhance nitric oxide-induced cell death in U937 cells

Nitric oxide (NO), a radical species produced by many types of cells, is known to play a critical role in many regulatory processes, yet it may also participate in collateral reactions at higher concentrations, leading to cellular oxidative damage. The protective role of antioxidant enzymes against NO-induced oxidative damage in U937 cells was investigated in control and cells pre-treated with diethyldithiocarbamic acid, aminotriazole, and oxlalomalate, specific inhibitors of superoxide dismutase, catalase, and NADP(+)-dependent isocitrate dehydrogenase, respectively. Upon exposure to 1 mM S-nitroso-N-acetylpenicillamine (SNAP), the nitric oxide donor, to U937 cells, the viability was lower and the protein oxidation, lipid peroxidation and oxidative DNA damage reflected by an increase in 8-hydroxy-2'-deoxyguanosine, were higher in inhibitor-treated cells as compared to control cells. We also observed the significant increase in the endogenous production of reactive oxygen species, as measured by the oxidation of 2'7'-dichlorodihydrofluorescin as well as the significant decrease in the intracellular GSH level in inhibitor-treated U937 cells upon exposure to NO. Upon exposure to 0.2 mM SNAP, which induced apoptotic cell death, a clear inverse relationship was observed between the control and inhibitor-treated U937 cells in their susceptibility to apoptosis. These results suggest that antioxidant enzymes play an important role in cellular defense against NO-induced cell death including necrosis and apoptosis.

Magnetic resonance elastography with twin drivers for high homogeneity and sensitivity

Magnetic Resonance Elastography (MRE) is a phase-contrast technique using conventional Magnetic Resonance Imaging system to visualize propagating shear waves and study the stiffness of tissues. Usually, shear vibrations are applied to the surface of tissues by means of mechanical driver at one point. But it is hard for the single driver to detect very small tumors. Multiple drivers are expected to provide better elastogram and to be more sensitive to the small stiff inclusions. In this study, a pair of drivers was used and compared with the single driver. The result shows that using the twin drivers is more sensitive to small hard inclusions than using single driver. It is expected that the twin drivers can detect small tumors in tissues which can hardly be detected by a single driver. Further study will be conducted with the twin drivers in ex-vivo and in-vivo studies.

Needle shear wave driver for magnetic resonance elastography

Magnetic resonance elastography (MRE) is capable of quantitatively depicting the mechanical properties of tissues in vivo. In contrast to mechanical excitation at the surface of the tissue, the method proposed in this study describes shear waves produced by an inserted needle. The results demonstrate that MRE performed with the needle driver provides shear stiffness estimates that correlate well with those obtained using mechanical testing. Comparisons between MRE acquisitions obtained with surface and needle drivers yielded similar results in general. However, the well-defined wave propagation pattern provided by the needle driver in a target region can reduce section orientation-related error in wavelength estimation that occurs with surface drivers in 2D MRE acquisitions. Preliminary testing of the device was performed on animals. This study demonstrates that the needle driver is an effective option that offers advantages over surface drivers for obtaining accurate stiffness estimates in targeted regions that are accessible by the needle.

Protective role of superoxide dismutases against ionizing radiation in yeast

The protective role of superoxide dismutases (SODs) against ionizing radiation, which generates reactive oxygen species (ROS) harmful to cellular function, was investigated in the wild-type and in mutant yeast strains lacking cytosolic CuZnSOD (sod1Delta), mitochondrial MnSOD (sod2Delta), or both SODs (sod1Deltasod2Delta). Upon exposure to ionizing radiation, there was a distinct difference between these strains in regard to viability and the level of protein carbonyl content, which is the indicative marker of oxidative damage to protein, intracellular H2O2 level, as well as lipid peroxidation. When the oxidation of 2',7'-dichlorofluorescin was used to examine the hydroperoxide production in yeast cells, the SOD mutants showed a higher degree of increase in fluorescence upon exposure to ionizing radiation as compared to wild-type cells. These results indicated that mutants deleted for SOD genes were more sensitive to ionizing radiation than isogenic wild-type cells. Induction and inactivation of other antioxidant enzymes, such as catalase, glucose 6-phosphate dehydrogenase, and glutathione reductase, were observed after their exposure to ionizing radiation both in wild-type and in mutant cells. However, wild-type cells maintained significantly higher activities of antioxidant enzymes than did mutant cells. These results suggest that both CuZnSOD and MnSOD may play a central role in protecting cells against ionizing radiation through the removal of ROS, as well as in the protection of antioxidant enzymes.

Tight binding of pyridoxal 5'-phosphate to recombinant Escherichia coli pyridoxine 5'-phosphate oxidase

Escherichia coli pyridoxine (pyridoxamine) 5'-phosphate oxidase (PNPOx) catalyzes the oxidation of pyridoxine 5'-phosphate and pyridoxamine 5'-phosphate to pyridoxal 5'-phosphate (PLP) using flavin mononucleotide (FMN) as the immediate electron acceptor and oxygen as the ultimate electron acceptor. This reaction serves as the terminal step in the de novo biosynthesis of PLP in E. coli. Removal of FMN from the holoenzyme results in a catalytically inactive apoenzyme. PLP molecules bind tightly to both apo- and holoPNPOx with a stoichiometry of one PLP per monomer. The unique spectral property of apoPNPOx-bound PLP suggests a non-Schiff base linkage. HoloPNPOx with tightly bound PLP shows normal catalytic activity, suggesting that the tightly bound PLP is at a noncatalytic site. The tightly bound PLP is readily transferred to aposerine hydroxymethyltransferase in dilute phosphate buffer. However, when the PNPOx. PLP complex was added to aposerine hydroxymethyltransferase suspended in an E. coli extract the rate of reactivation of the apoenzyme was several-fold faster than when free PLP was added. This suggests that PNPOx somehow targets PLP to aposerine hydroxymethyltransferase in vivo.

Abnormal regulation of DNA methyltransferase expression during colorectal carcinogenesis

Somatic changes in CpG dinucleotide methylation occur quite commonly in human cancer cell DNA. Relative to DNA from normal human colonic cells, DNA from human colorectal cancer cells typically displays regional CpG dinucleotide hypermethylation amid global CpG dinucleotide hypomethylation. The role of the maintenance DNA methyltransferase (DNMT1) in the acquisition of such abnormal CpG dinucleotide methylation changes in colorectal cancer cells remains controversial; in one study, 60-200-fold increases in DNMT1 mRNA expression were detected in colorectal polyps and cancers relative to normal colonic tissue [W. S. El-Deiry et al., Proc. Natl. Acad. Sci. USA, 88: 3470-3474, 1991], whereas in another study, only small increases in DNMT1 mRNA expression, commensurate with differences in cell proliferation accompanying colonic tumorigenesis, were observed [P. J. Lee et al., Proc. Natl. Acad. Sci. USA, 93: 10366-10370, 1996]. To definitively ascertain whether abnormal DNMT1 expression might accompany human colorectal carcinogenesis, we subjected a series of normal and neoplastic colonic tissues to immunohistochemical staining using a polyclonal antiserum raised against a DNMT1 polypeptide. A concordance of DNMT1 expression with the expression of PCNA and other cell proliferation markers, such as Ki-67 and DNA topoisomerase IIalpha, was observed in normal colonic epithelial cells and in cells comprising other normal epithelia and lymphoid tissues. The polypeptide p21, which has been reported to undermine DNMT1 binding to proliferating cell nuclear antigen at DNA replication sites, was not expressed by normal colonic cells containing DNMT1 and other cell proliferation markers. In adenomatous polyps, although DNMT1 expression coincided with the expression of other cell proliferation markers, many DNMT1-expressing cells also expressed p21. The fidelity of DNMT1 expression was further undermined in colorectal carcinomas, in which a striking heterogeneity in DNMT1 expression, with some carcinoma cells containing very high DNMT1 levels and others containing very low DNMT1 levels, was observed. These results indicate that human colorectal carcinogenesis is accompanied by a progressive dysregulation of DNMT1 expression and suggest that abnormalities in DNMT1 expression may contribute to the abnormal CpG dinucleotide methylation changes characteristic of human colorectal carcinoma cell DNA.

Down regulation of extramacrochaetae mRNA by a Drosophila neural RNA binding protein Rbp9 which is homologous to human Hu proteins

Rbp9 is an RNA binding protein expressed mainly in the central nervous system of adult Drosophilamelanogaster. Rbp9 shares a high degree of sequence similarity with human neural proteins referred to as Hu antigens. Hu antigens bind to U-rich mRNA destabilizing elements with a high affinity and, thus, have been implicated as regulators of mRNA stability. Using in vitro RNA binding assays, we found that Rbp9 binds strongly to poly U sequences. We then employed a Selex system to identify a consensus Rbp9 binding site (UUUXUUUU). Information obtained from the Selex results allowed the detection of two repeats of the Rbp9 consensus binding sequence in the 3' untranslated region of extramacrochaetae mRNA. UV crosslinking experiments demonstrated that Rbp9 interactsspecifically with emc mRNA. The requirement of Rbp9 protein in the down regulation of emc mRNA was confirmed by northern (RNA) analysis, which revealed that the level of emc mRNA increased 10-fold in rbp9 mutant flies. Taken together with the in vitro RNA binding results, the genetic evidence obtained strongly supports the hypothesis that Rbp9 functions as a regulator of RNA stability.

Selenocysteine tRNAs as central components of selenoprotein biosynthesis in eukaryotes

Selenocysteine (Sec) tRNAs serve as carrier molecules for the biosynthesis of Sec from serine and to donate Sec to protein in response to specific UGA codons. In this study, we describe the current status of Sec tRNAs in higher animals and further we examine: (i) the Sec tRNA population in Drosophila; (ii) transcription of the Sec tRNA in vivo (in Xenopus oocytes) and in vitro (in Xenopus oocyte extracts); (iii) the effect of selenium on the Sec tRNA population in various rat tissues following replenishment of extremely selenium deficient rats with this element; and (iv) the biosynthesis of the modified bases on Sec tRNA in Xenopus oocytes.

Analysis of the selenocysteine tRNA[Ser]Sec gene transcription in vitro using Xenopus oocyte extracts

An in vitro transcription system was devised using a Xenopus oocyte S150 extract for analyzing expression of the Sec tRNA[Ser]Sec gene. The activator element, located at about -200 that is required for maximal expression of the tRNA[Ser]Sec gene in vivo, had no effect on tRNA[Ser]Sec transcription in vitro. In vitro transcription of this gene even tolerated mutations within or deletion of the PSE, showing marked contrast with the requirements observed in vivo. However, the TATA box was indispensable for basal level expression of the gene both in vivo and in vitro. The region spanning from the TATA box to the transcription start point (-33 to -1) was sufficient for Pol III to recognize the tRNA[Ser]Sec gene promoter in vitro.