SHE'S the most successful and extreme star of America's porn industry. A self-styled pioneer of female sexual freedom; an existentialist with a love of Jean- Luc Godard; and now, in Edinburgh, she is about to achieve a world first: becoming the first actress to successfully cross over from hardcore movies to mainstream cinema.

Welcome to the world of Sasha Grey.

Grey, who hails from Sacramento, California, has starred in more than 150 hardcore films, including The Apprentass, Superslut and Fashionistas - the biggest-budget porn film ever made. Later this year, she will star in the new film directed by cult art-house auteur, Steven Soderbergh, of Sex, Lies And Videotape fame, which is to have its UK premiere at the Edinburgh International Film Festival.

The film is aptly titled The Girlfriend Experience, an expression coined in the sex industry by male customers who pay for a prostitute to act like a girlfriend. To make the leap from porn to mainstream movies is all but unheard of, but to make the leap from porn to arthouse cinema with a world-class director is the Holy Grail for any porn star or starlet.

So how did Grey do it? "Actually, one of his Soderbergh's writers contacted me though MySpace," she said. "He said, We read an article on you and Steven Soderbergh would love to meet you to discuss a project. Obviously, it's MySpace so I didn't believe it, and I said, Well, how am I supposed to know this is really you and that you're really affiliated with him?'. He said, I'll have him leave you a voicemail.' "And he did, so I met with up with him at the Warner offices, and he discussed the project. It was really simple, and a year and a half later we shot the film."

The Girlfriend Experience was filmed on a comparatively tiny budget of just £1.15 million, on HD video using natural daylight. Most of the action was improvised by the cast and captured by a crew of just a dozen.

Grey plays Christine, a high-end Manhattan escort who goes by the business name of Chelsea.

The movie follows Christine's professional life, the lucrative services she offers, and the impact it has on her struggling personal trainer and boyfriend played by Chris Santos.

Grey said: "The beauty of this film, in the way it was filmed, is that it allows the viewer to read into things. Coming from a person who acted in the film and was on set every day, I think to me that's one of the je ne sais quoi's about the film. But I think she Chelsea likes to separate the personal and professional, and she would rather not talk about the professional."

So does the 21-year-old Grey appreciate the parallel lives of a porn star and a call girl?

"The difference between me and that character is that I don't really see a difference between my personal and quote unquote professional lives," she said. "A lot of people have said, My life is my art,' and that's the way I look at it. I don't go home at the end of the day and kick off my heels and turn off the lights and go into another headspace.

"It's all-inclusive, and I don't look at it as just a career. I look at it as my life."

Grey's on-screen incarnations are noted for their extreme sexuality. She has pushed the boundaries of what is acceptable even by the standards of American porn. As a porn star she represents herself, keeping control of her career, and has won numerous AVN awards - the porn equivalent of the Oscars. Her success, openness and flouting of the conventional view of porn starlets as victims has made her an icon.

Her MySpace biography says: "I grew up in North Highlands. It is a disenfranchised, lower-to-middle class neighbourhood. I never allowed myself to be a negative product of that environment. I used it as a source of inspiration to challenge myself.

"The acts I perform are always consensual. I am a woman who strongly believes in what she does - it is time that our society comes to grips with the fact that normal people, women especially, enjoy perverse sex.

"I am ready to take on any opportunities and challenges that face me as a woman, porn star, and artist."

The Girlfriend Experience debuts at Cineworld in Dundee Street, Edinburgh on June 24