The words ''Kate Upton'' and ''serious actor'' probably won't be seen in the same sentence in the foreseeable future. But the Sports Illustrated swimsuit model who turned 21 on the set of her feature film debut, The Other Woman, seems eager to challenge that stereotype.

''I was bitten a little by an acting bug so I took acting classes for two years,'' she offers as evidence the move is more than a whim. ''Now I'm full in, I love it!''

The perky American's long blonde hair is pulled back in a ponytail and she is wearing little make-up and no jewellery. As she fidgets with her clasped hands on the table during our chat in a Los Angeles hotel suite, it's evident she has a tiny cross tattooed between her fingers and another tattoo of a small horseshoe placed sideways on a wrist.

''This is for luck and also to remind me of horse showing,'' the prize-winning equestrian explains proudly of the horseshoe. ''It's also crooked so I don't lose my luck. And then the cross is because I am religious, and in modelling you can't really wear necklaces that much because you have to take everything off, so I always wanted a cross with me.''

It's hard to juxtapose the image of a pious churchgoer with the Kate Upton who has websites devoted to her, um, two biggest assets and a social media presence that includes two provocative boob-jiggling dance videos that went viral on YouTube. Leslie Mann, Upton's co-star in The Other Woman, insists the young hyphenate is not one thing or the other.

''She's just a baby - only five years older than my daughter - so at first I found myself feeling very protective of her,'' admits the 42-year-old actor and wife of comedy mogul Judd Apatow. ''But then I realised she's smarter than me: she's a great businesswoman, she's super funny and she has a great attitude on set, so she must have had great parents.''

In The Other Woman, Upton, Mann and Cameron Diaz play three women who bond over a plan to get revenge on the man who cheated on them all. Carly (Diaz) is a tough New York lawyer who makes a surprise visit to the home of her boyfriend, Mark (Nikolaj Coster-Waldau), and discovers he is married to devoted housewife Kate (Mann). Carly and Kate barely have time to process the existence of each other when they find out about a third woman, Amber (Upton), who is also caught up in Mark's lies.

Upton, who has said she's too busy focusing on her career to have a serious relationship of her own, says: ''My parents are still married and my grandparents are still married, so for me, marriage means a lot. And I think that's the connection with my character, that she wouldn't ever have been with him if she knew that he was married.''

Upton grew up in a conservative home in the city of Melbourne, Florida, with a mother who was a former tennis champion and a father who was a high school athletics director, so physical activity was important. The niece of Republican congressman Fred Upton attended Holy Trinity Episcopal Academy and was pursuing an equestrian career when it was derailed by an introduction to modelling.

''I was 12 and I was leaving a horse show and someone scouted me and my mom was like, 'no way, she's too young','' Upton recalls. ''But I just got this idea in my mind and I started researching it.''

She began modelling three years later, moving to New York and immediately making the covers of top fashion magazines before she landed the cover of last year's Sports Illustrated Swimsuit Issue, shot in Antarctica and featuring Upton wearing only a white bikini bottom and nothing underneath a partially open fur-hooded white winter jacket.

Diaz says she and Upton bonded over their modelling backgrounds during the beachside shoot in the Hamptons, Long Island. ''I turned 21 on the set of my first film, The Mask, and she reminds me of myself at that age in some ways,'' the 41-year-old actor muses. ''The great thing about Kate is that she doesn't care about any of this shit; she's just in it and having a good time, and that's a really good place to be at her age.''

Upton seems unperturbed by the critics who dismiss her acting ambitions: ''It actually makes it easier when people underestimate you.'' Beware of the dumb blonde exterior, she warned in an interview last year with Elle magazine. ''People deal with models like they are children. I'm always like: 'I'm about to pull something over on you, and you're so focused on thinking I'm dumb, you're not even going to know!' ''

Catwalk to screen

Kate Upton is in good company as a model turned actress. As well as Cameron Diaz, her co-star in The Other Woman and a one-time covergirl of Seventeen magazine, are others including:

Brooke Shields - The youngest model to appear on the cover of Vogue at age 14, she wasted no time transitioning into films including Pretty Baby (1978), The Blue Lagoon (1980) and her hit TV show Suddenly Susan (1996-2000).

Andie MacDowell - Appeared on the cover of Vogue and in Calvin Klein commercials before making her mark in films including Sex, Lies and Videotape (1989), Groundhog Day (1993) and Four Weddings and a Funeral (1994).

Charlize Theron - After winning a local modelling contest in South Africa at age 16, the former dancer modelled her way around Europe and eventually moved to the US. Theron began acting and won an Oscar in 2003 for breaking the typecast as a gay serial killer in Monster.

Freida Pinto - A former runway model and magazine cover girl in India, Pinto's debut acting role in the 2008 Oscar hit Slumdog Millionaire has led to more films, including Immortals (2011) and Rise of the Planet of the Apes (2011).

Halle Berry - The former 1986 Miss USA runner-up modelled her way into Hollywood, playing Storm in the 2000 blockbuster X-Men and becoming the first African American to take home a best actress Oscar for her role in Monster's Ball (2001).

Elizabeth Hurley - Hurley didn't turn to modelling until she was 29 but quickly became a ''spokesmodel'' for beauty company Estee Lauder and went on to make films such as Austin Powers: International Man of Mystery (1997) and Bedazzled (2000).

Vanessa Williams - After resigning her 1984 Miss America crown when nude photos surfaced in Penthouse, Williams became a top model, recording artist and then actress who starred in the TV comedy Ugly Betty (2006-10) and joined Desperate Housewives for its final two seasons (2010-12).

Cybill Shepherd - At 16, she won the Miss Teenage Memphis contest and at 18 was Model of the Year. Her first film, The Last Picture Show (1971), was a hit but Shepherd made her biggest mark in the detective series Moonlighting (1985-1989) alongside Bruce Willis.

The Other Woman is released in cinemas on April 17.