June-Sok Lee

Prevention of premature senescence requires JNK regulation of Bcl-2 and reactive oxygen species

Premature senescence is considered as a cellular defense mechanism to prevent tumorigenesis. Although recent evidences show that c-Jun N-terminal kinase (JNK) is involved in the senescence process, the mechanism for this regulation is not fully understood. Here, we examined the role of JNK in premature senescence of tumor cells. Treatment of cells with the JNK-specific inhibitor SP600125 caused phenotypical changes of senescence and triggered a rapid increase in mitochondrial reactive oxygen species (ROS) production and DNA-damage response (DDR) in MCF7 breast carcinoma cells. ROS generation was attributed to the suppression of B-cell lymphoma-2 (Bcl-2) phosphorylation, and resulted in DNA damage and p53 activation. Bax did not change their localization to the mitochondria, which is required for apoptosis. The essential roles of JNK and phosphorylated Bcl-2 in preventing premature senescence were confirmed using RNA interference and ectopic expression of mutants of Bcl-2, including phosphomimetic and nonphosphorylatable forms. These findings were evidenced in H460 lung carcinoma cells and primary human embryonic fibroblasts. Altogether, our results showed that loss of JNK activity triggers a Bcl-2/ROS/DDR signaling cascade that ultimately leads to premature senescence, indicating that basal JNK activity is essential in preventing premature senescence.

A video camera system with adaptive zoom tracking

This paper presents an advanced auto focus camera system using the adaptive zoom tracking method. The proposed system can achieve an accurate zoom tracking with significantly reduced system memory.

A burst error concealment technique for visual communications in a mobile environment

A burst error concealment technique is proposed for visual communications in a mobile environment. The proposed method is applicable to wireless visual communications due to its low computational cost and acceptable image quality. In the transmission of real-time video over wireless, due to the limited bandwidth available, a frame is divided into just 2 or 3 packets. Therefore, the loss of a packet introduces burst errors which are the loss of the several rows of macroblocks (MBs) in the frame. The proposed error concealment technique estimates the lost motion vector (MV) by using the neighboring MVs of the damaged MB.

Noise-Robust Modulation Identification Method for Adaptive Receiver Based on Software Defined Radio

In this paper, we propose an effective noise- robust modulation identification algorithm for adaptive receiver based on software defined radio. The proposed method can estimate the carrier frequency, symbol rate, and modulation scheme of the received signal without the use of the handshaking process requiring supplementary information such as the training sequence. Experimental results show that the proposed algorithm demodulates the signal with a low probability of error at the noisy channel conditions.

An effective motion vector re-estimation method for low bit-rate video transcoding

For the low bit-rate multimedia communications, video contents have to be transcoded according to the requirements of network bandwidth and the performance of clients. However, transcoding to the low bit-rate creates video quality degradation (drift error) caused by quantization, motion vector truncation, and downsizing. In this paper, we present an effective motion vector re-estimation method to compensate drift errors in the spatial resolution reduction transcoding. Experimental results show that our method can preserve image quality while transcoding to the low bit-rate.

Effective drift reduction technique for reduced bit-rate video adaptation

Video transcoding to the low bitrate creates drift error caused by quantization, motion vector mapping, and texture downsizing. In this paper, we propose a drift reduction technique for spatial resolution reduction transcoding. The proposed technique uses adaptive motion mapping and refinement for avoiding the generation of the drift error and forced skipping of macroblock encoding for terminating the propagation of drift error. Experimental results show that proposed technique can preserve image quality while transcoding to the low bitrate.

An advanced camera system having fast autofocus control

This paper presents an advanced camera system which performs a fast autofocus control under different scene situations. Experimental results demonstrate that proposed system can find the in-focus lens position precisely without the influence of noise.

Residual Motion Coding Method for Error Resilient Transcoding System

For video adaptation in universal multimedia access systems, video contents have to be transcoded according to the requirements of network bandwidth and the performance of clients. However, the transcoded video streams are vulnerable to channel disturbances when they are transmitted over the wireless channels. In this paper, we present an error resilient transcoding system using the residual motion coding method for wireless visual communications networks. The residual motion coding method interleaves into the bitstream the residual motion vector that is auxiliary motion information to be used at the decoder to recover the lost motion vector. With the residual motion vector, the decoder can precisely reproduce the motion vector of the corrupted macroblock and reconstruct the lost macroblock by using error concealment based on temporal prediction. Experimental results show that the proposed method can not only achieve the error robustness of the motion vector, but also improve the performance of error concealment at the decoder.